What happens if i forget to degrease wheels before painting?
I’m going to take a wild guess 
and state that the paint will not adhere very well or for very long.
Just think of it as a practice run for when you get to do it again soon when the paint falls off…
You live and you learn, as long as you learn from your mistakes…
Why are wheels greasy? I’d make a wild assumption wheels might be dirty prior to painting. You did clean them first? Preparation is 90% of any paint job.