It's Obvious Now
The enemy we are fighting casts Invisibility, and disappears from view. This causes some problems with those in the party who are incompetent enough not to be able to cast See Invisibility.
'I don't know what I can do against an invisible enemy. I suppose I'll have to be on the defensive until the spell wears off.'
'How about casting Dispel Magic?'
'It's a good idea, but where would I target the spell?'
'On the invisible chap!'
'...'