I tend to jot down moments, lines, interactions that don't really make any sense. I try and explain these scattered notes to my close friends, and they become more and more logical. I see screenwriting as a bit like a math equation which I have to solve.
I think sometimes we look at other people's marriages and we think they must always be so happy together. I don't know anybody who's married for a long time who hasn't somehow made room in their love story for the hate and resentment that they sometimes feel toward each other.