Adulthood over Childhood

So, I'm wondering how long it takes for the Reason of Adulthood to overcome the Emotion of Childhood?  All these "lessons" I learned as a child -- Be nice.  Be polite.  Don't yell.  Act like a lady.  Do it yourself. Be happy.  -- have not served me well as an adult.  These little mantras set me up for failure in adult relationships.  The Truth is much easier to work with than Nice.  What is the advantage or benefit of acting like a lady?  When doing everything for myself, I don't learn how to lean on someone or ask for help when I do need it.  And "be happy"? Seriously? What the fuck? Life is not always happy.  Deal.
My husband tried for years to get me to quit being nice and polite and doing it myself.  I'm passive-aggressive enough that he saw right through me, but I still wouldn't put it into action.  I held onto thinking these stupid bumpersticker were the way I had to be.  If I say out loud "I am not happy" then horrible things might happen.  Like he might quit liking me.  Actually, he probably would have like me more because we together could have fixed why I wasn't happy and then I might have been happy and he might have been happy and we might have been happy together.  Instead, I acted out, had an affair and now we really, truly are not happy.  Some days are better than others and overall I believe we're getting better.
Why did those ways of being that I picked up as a child hold on so tightly?  Why didn't I see Reason when I was an adult, making adult choices and being away from my family?  It frightens me to think what I've done to my own kids.