Are Illusionists subject to their own illusions?

Question

In general, does the caster of a visual illusion experience the full effect of that illusion? For example, Minor Illusion can create an un-moving illusory object that seemingly everyone can see. Would this object be as opaque for the caster, or more faint, as it would appear to someone who successfully investigated the illusion?

For example, if an illusionist created the appearance of a brick wall between himself and some attackers, would the illusionist still be able to see the attackers? Or would the illusionist have to use an action to Investigate his own illusion first?

Answer 1

Minor Illusion has the following sentence, and most other illusion spells have a similar one:

If a creature discerns the illusion for what it is, the illusion becomes faint to the creature.

Given that the caster created the illusion, and should therefore be able to discern it for what it is, this suggests that the illusion will be faint for the caster. On the other hand, let's look at it with a bit more context:

If a creature uses its action to examine the sound or image, the creature can determine that it is an illusion with a successful Intelligence (Investigation) check against your spell save DC. If a creature discerns the illusion for what it is, the illusion becomes faint to the creature.

This paragraph, taken as a whole, suggests that examining the illusion is what causes it to become faint, so there's definitely some ambiguity here.

So, if you're a player, the answer is, as always, ask your DM. They get to make the final decision here, and even if the rules were unambiguously one way or the other, they would still have the veto.

If you're the DM, on the other hand, it's up to you. Personally, I'd be inclined to rule in favour of the players here; it's much less likely to cause fights.

Answer 2

No, it does not affect the caster

The reason is quite simple, as stated in the rules:

If a creature discerns the illusion for what it is, the illusion becomes faint to the creature.

The key part for the caster is highlighted. Without a single shred of doubt, the caster knows what it is, therefore the caster is not affected.

Another proof, a longer one, would be looking on how some illusions, in particular this illusion, are found out. An extract from Silent Image:

Physical interaction with the image reveals it to be an illusion, because things can pass through it.

And from Disguise Self

The changes wrought by this spell fail to hold up to physical inspection.

The way illusions are found out is by investigation. And that talks about the thought process that it is needed to reach the conclusion that the illusion is, in fact, an illusion. The affected creature needs a reason to believe that what he is seeing is an illusion, the caster does not:

A strange statue in an art museum would not trigger the need to investigate but same statue in your room, where it was not before, is a reason to investigate. The narrative in some cases is "the hand passes through the object", but it can also be "Bob, with his innate talent to bypass the most mundane situation, was exceptionally sharp this time. He discover the shimmer that the wizard always forget to take out".

Everything in the arsenal of the illusions point out the need for an ignorant target. A target that can't discern, figure it out, knows, that the presented phenomena is an illusion. You are not ignorant on your own doings, at least not in this case. It is a direct consequence of your actions and, therefore, your illusions do not affect you. Sadly for your comrades they always doubt, cursing you for being better and better at it as you gain experience.

Answer 3

Knowing that something is an illusion does not change any of its in game effects, except as allowed for in the spell description. And how you know it is an illusion is also spelled out in the description: illusions are powerful magic that deceive the mind and/or senses, intellectual knowledge that you are being affected by magic is not enough to stop the effect.

For Minor Illusion

Physical interaction with the image reveals it to be an illusion, ...

If a creature uses its action to examine the sound or image, the creature can determine that it is an illusion with a successful Intelligence (Investigation) check against your spell save DC. If a creature discerns the illusion for what it is, the illusion becomes faint to the creature.

There is nothing in there along the lines of "if you cast the spell you know it is an illusion" so an illusionist's senses are just as comprehensively affected by their own magic as anybody else's. Thinking of it as the difference between knowing it is an illusion academically and knowing it is an illusion viscerally.

The illusionist does have the advantage that they can wave their hand through it to prove to their guts what their mind already knows.