I think it's normal - I try to write character profiles (general description, motivations, past experiences) then decide on a few events, then use the characters' profiles to fill in the blanks -

So if the house catches fire, Donny would likely run for his life, forsaking anyone else to fend for themselves, but Megan would definitely try to save every living soul within. Then when everyone is safe and the fire department arrives, she doesn't chastise him because she knows he has a troubled past filled with tragic situations where his life has been threatened... But he feels the need to apologize and make amends...

Etc.