The root cause is a failure to understand that Actions are not all-encompassing.

The rules list 5 activities that you can do On Your Turn:

On your turn, you can move a distance up to your speed and take one action.

Bonus Actions

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

...

Other Activity on Your Turn

Your turn can include a variety of flourishes that require neither your action nor your move.

You can communicate however you are able, through brief utterances and gestures, as you take your turn.

You can also interact with one object or feature of the environment for free, during either your move or your action.

...

Reactions

Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

To reiterate, the 5 activities are:

1. Move
2. Actions
3. Bonus Actions (which are not a type of 'action')
4. Other Activities (a class containing all miscellaneous activities) including;

• Brief communication
• Object interaction
• Broadly, anything that "does not require an action"

5. Reactions (with a note that they can be used on someone else's turn).

Of these activities only 1 of them is an "Action". This confusion and resulting mistaken assumption that everything you do on your turn is an Action has lead to a lot of fundamental misunderstandings about how 5e works.

A special note for Bonus Action:

Bonus Actions are not Actions. They let you take an Action, usually from a select list. "Let" means you have the option, you are allowed to. It does not mean that Bonus Actions are actions.

Read Bonus Action again:

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

Some people misread this as "an additional action ... called a bonus action". However this is incorrect. The additional action is not the "bonus action". The "bonus action" is what enables you to take the additional action: "[Various class features, spells, and other abilities let you take an additional action on your turn] called a bonus action." The action isn't a normal action, it is a resulting effect of these class features, spells, and other abilities.

An example, Cunning Action:

Starting at 2nd level, your quick thinking and agility allow you to move and act quickly. You can take a bonus action on each of your turns in combat. This action can be used only to take the Dash, Disengage, or Hide action.

Try and understand Bonus Action's text in the context of Bonus Action: Cunning Action lets you take an additional action on your turn, it is a bonus action.

Now it becomes obvious that Cunning Action is a "Bonus Action" and it lets you take an "additional Action". Cunning Action is NOT an Action. Neither are Bonus Actions an Action.

The root cause is a failure to understand that Actions are not all-encompassing.

The rules list 5 activities that you can do On Your Turn:

On your turn, you can move a distance up to your speed and take one action.

Bonus Actions

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

...

Other Activity on Your Turn

Your turn can include a variety of flourishes that require neither your action nor your move.

You can communicate however you are able, through brief utterances and gestures, as you take your turn.

You can also interact with one object or feature of the environment for free, during either your move or your action.

...

Reactions

Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

To reiterate, the 5 activities are:

1. Move
2. Actions
3. Bonus actions
4. Other activities (a class containing all miscellaneous activities) including;

• Brief communication
• Object interaction
• Broadly, anything that "does not require an action"

5. Reactions (with a note that they can be used on someone else's turn).

Of these activities only 1 of them is an "Action". This confusion and resulting mistaken assumption that everything you do on your turn is an Action has lead to a lot of fundamental misunderstandings about how 5e works.

A special note for bonus action:

There are different rules for actions and bonus actions. You can think of bonus actions as a special way to perform actions. Just be aware that there are different rules and limitations for both of them.

The root cause is a failure to understand that Actions are not all-encompassing.

The rules list 5 activities that you can do On Your Turn:

On your turn, you can move a distance up to your speed and take one action.

Bonus Actions

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

...

Other Activity on Your Turn

Your turn can include a variety of flourishes that require neither your action nor your move.

You can communicate however you are able, through brief utterances and gestures, as you take your turn.

You can also interact with one object or feature of the environment for free, during either your move or your action.

...

Reactions

Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

To reiterate, the 5 activities are:

1. Move
2. Actions
3. Bonus Actions (which are not a type of 'action')
4. Other Activities (a class containing all miscellaneous activities) including;

• Brief communication
• Object interaction
• Broadly, anything that "does not require an action"

5. Reactions (with a note that they can be used on someone else's turn).

Of these activities only 1 of them is an "Action". This confusion and resulting mistaken assumption that everything you do on your turn is an Action has lead to a lot of fundamental misunderstandings about how 5e works.

A special note for Bonus Action:

Bonus Actions are not Actions. They let you take an Action, usually from a select list. "Let" means you have the option, you are allowed to. It does not mean that Bonus Actions are actions.

The root cause is a failure to understand that Actions are not all-encompassing.

The rules list 5 activities that you can do On Your Turn:

On your turn, you can move a distance up to your speed and take one action.

Bonus Actions

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

...

Other Activity on Your Turn

Your turn can include a variety of flourishes that require neither your action nor your move.

You can communicate however you are able, through brief utterances and gestures, as you take your turn.

You can also interact with one object or feature of the environment for free, during either your move or your action.

...

Reactions

Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

To reiterate, the 5 activities are:

1. Move
2. Actions
3. Bonus Actions (which are not a type of 'action')
4. Other Activities (a class containing all miscellaneous activities) including;

• Brief communication
• Object interaction
• Broadly, anything that "does not require an action"

5. Reactions (with a note that they can be used on someone else's turn).

Of these activities only 1 of them is an "Action". This confusion and resulting mistaken assumption that everything you do on your turn is an Action has lead to a lot of fundamental misunderstandings about how 5e works.

A special note for Bonus Action:

Bonus Actions are not Actions. They let you take an Action, usually from a select list. "Let" means you have the option, you are allowed to. It does not mean that Bonus Actions are actions.

Read Bonus Action again:

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

Some people misread this as "an additional action ... called a bonus action". However this is incorrect. The additional action is not the "bonus action". The "bonus action" is what enables you to take the additional action: "[Various class features, spells, and other abilities let you take an additional action on your turn] called a bonus action." The action isn't a normal action, it is a resulting effect of these class features, spells, and other abilities.

An example, Cunning Action:

Starting at 2nd level, your quick thinking and agility allow you to move and act quickly. You can take a bonus action on each of your turns in combat. This action can be used only to take the Dash, Disengage, or Hide action.

Try and understand Bonus Action's text in the context of Bonus Action: Cunning Action lets you take an additional action on your turn, it is a bonus action.

Now it becomes obvious that Cunning Action is a "Bonus Action" and it lets you take an "additional Action". Cunning Action is NOT an Action. Neither are Bonus Actions an Action.

The root cause is a failure to understand that Actions are not all-encompassing.

The rules list 5 activities that you can do On Your Turn:

On your turn, you can move a distance up to your speed and take one action.

Bonus Actions

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

...

Other Activity on Your Turn

Your turn can include a variety of flourishes that require neither your action nor your move.

You can communicate however you are able, through brief utterances and gestures, as you take your turn.

You can also interact with one object or feature of the environment for free, during either your move or your action.

...

Reactions

Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

To reiterate, the 5 activities are:

1. Move
2. Actions
3. Bonus Actions (which are not a type of 'action')
4. Other Activities (a class containing all miscellaneous activities) including;

• Brief communication
• Object interaction
• Broadly, anything that "does not require an action"

5. Reactions (with a note that they can be used on someone else's turn).

Of these activities only 1 of them is an "Action".

Bonus Actions do have a similar name, and they often let you perform an Action, but they are not themselves Actions.

This confusion and resulting mistaken assumption that everything you do on your turn is an Action has lead to a lot of fundamental misunderstandings about how 5e works.

The root cause is a failure to understand that Actions are not all-encompassing.

The rules list 5 activities that you can do On Your Turn:

On your turn, you can move a distance up to your speed and take one action.

Bonus Actions

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.

...

Other Activity on Your Turn

Your turn can include a variety of flourishes that require neither your action nor your move.

You can communicate however you are able, through brief utterances and gestures, as you take your turn.

You can also interact with one object or feature of the environment for free, during either your move or your action.

...

Reactions

Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

To reiterate, the 5 activities are:

1. Move
2. Actions
3. Bonus Actions (which are not a type of 'action')
4. Other Activities (a class containing all miscellaneous activities) including;

• Brief communication
• Object interaction
• Broadly, anything that "does not require an action"

5. Reactions (with a note that they can be used on someone else's turn).

Of these activities only 1 of them is an "Action". This confusion and resulting mistaken assumption that everything you do on your turn is an Action has lead to a lot of fundamental misunderstandings about how 5e works.

A special note for Bonus Action:

Bonus Actions are not Actions. They let you take an Action, usually from a select list. "Let" means you have the option, you are allowed to. It does not mean that Bonus Actions are actions.