Playing an insane character can be challenging, but there are potential rewards to be had. When the heroes seek out a reclusive sage, or a helpful wizard, or even the king of the land to have a serious chat about the hobgoblin armies forming on the borders, it can come as a bit of a shock when they slowly realise that this important and significant NPC who wields great power or has access to vital information... isn't entirely there.

How they end up dealing with this problem can be entertaining, and may even be a mini-quest unto itself.

Transcript

Palpatine: Give me his laser sword.
Palpatine: So uncivilised.
Luke: We've seen the Moon plans. Peaceful? Impossible.
Palpatine: Why, sometimes I've believed as many as six impossible things before breakfast.
{beat}
{beat}
Luke: You're mad. {to self in realisation, not direct accusation}
Palpatine: Oh, you can't help that; we're all mad here. I'm mad; you're mad.
Luke: Why do you think I'm mad?
Palpatine: You must be, or you wouldn't have come here.
R2-D2: He has a point.