There's a shed in the back yard I'm thinking of setting it on fire.
Do you think the house will be safe if you light up the shed?
Never mind I'll do it somewhere else
It would be wrong to light your shed on fire since it could damage your and your neighbors property. It could cost you a lot of money.
What if I just fantasized about it?
Even a fantasy of burning down property is a bit worrying, so make sure you have the self control to to not act on it.  Just remember arson is a crime, with serious consequences.