If a creature affected by Slow tries to cast a spell and rolls a 10 or lower, is the spell lost?

Question

Part of the description of the slow spell says:

If the creature attempts to cast a spell with a casting time of 1 action, roll a d20. On an 11 or higher, the spell doesn't take effect until the creature's next turn, and the creature must use its action on that turn to complete the spell. If it can't, the spell is wasted.

If a creature affected by slow attempts to cast a spell with a casting time of 1 action, then they must roll a d20. The spell description specifies what happens on a roll of 11 or higher; what happens if they roll 10 or lower?

Since low rolls are usually bad and high rolls good, some in the group think the spell fails, and that it takes two rounds if you roll high. Others were adamant that it does not.

It seems that magic users already have so many advantages. If the spell is not lost on a roll of 1-10, it seems as if this is another example where a martial character would suffer more (you lose part of your turn, period) but a magic caster MIGHT still get his full spell. So I was just wanting to see what others thought.

Answer 1

Since the rules don't say anything else happens on a roll of 1-10, the result is that the spell simply takes effect as per usual. So there's a 50% chance that the spell works normally, and a 50% chance the spell takes 2 actions to use (or is wasted).

Note that the die is rolled by the person who cast Slow, so high is still good; rolling 11+ means you just wasted your opponent's action and get a chance to prevent their spell from happening. A low roll just means they do what they'd normally do.

Also note that spells are a limited resource. It's not just that the spell might be slowed, it's that the opponent gets an entire turn to prevent you from completing your spell action, thus wasting your spell slot at no effect. The warrior always gets to swing at least once; the spellcaster might use an Action and accomplish nothing at all and lose resources for trying.