Who hasn't been in an old school D&D campaign with a power crazed wizard PC that casts Fireball, incinerates the monster... and his own party along with it. 

Wizard: I want to cast Fireball

DM: Okay, the room you are in is only 15' x 15'

Wizard: I didn't ask how big the room was, I said I want to cast Fireball

DM: Ooookay, everyone grab your D20 and roll your saving throw....