It's vs Its

It's fucking confusing. Well, not really, but I keep making mistakes anyhow. /r/ simple way to remember which is which.

The cat's food
The dog's food
Its food. <-- WHERE DID THE APOSTROPHE GO???

Its fat <-- The fat belongs to "it"
It's fat <-- It is obese
Sheila is fat <-- Sheila is obese
Sheila's fat <-- The fat belongs to Sheila
FUCKING PARADOX!!!

>>3
Thanks, but it didn't really make it any less confusing. Do I need to just "get it"? How much of an ass will I make of myself if I get this wrong in an official context?