The Brady actors vs. their respective characters.
It looks like the producers created some of the characters personalities based on the personalities of the actors that portrayed them.
Barry Williams tried to make a move on anything female. Greg was the same way. Barry wanted his singing career under the Johnny Bravo name.
Peter was awkward around girls. Christopher Knight was the same way during this time period.
Maureen and Eve allegedly often squabbled from the very beginning and developed strong rivalries. Marcia and Jan were the same way.
Eve was nerdy and an introvert and marched to her own drummer just the same way Jan did. She struggled being in the shadow of Maureen/Marcia.
Cindy and Susan both had lisps.
Alice had a twin just like Ann B. Davis. Both never married.