Say it's a vanilla oil plug-in. And say you plug it into a socket in your dining room before you go to bed. And say you don't really notice anything when you wake up because you're busy trying to not cough up a lung. (Thanks, bronchitis!) The fact that you didn't notice anything in the morning does not mean that you will not be knocked down by the cloying omnipresence of Vanilla Breeze when you arrive home from work at 5:35pm.
It seemed like a good idea.