I asked The Man what he thought made our marriage successful. We to and fro'd for a while and landed on this: I think we have compatible personalities. We have similar interest (which, may I point out, is not the same as the same interests!). We have slightly different skillsets - there are things he does well and there are things I do well, and in between we get most things done.
And something which is especially important to me: we leave each other a sense of freedom.
We don't set many expectations to each other and rather, strive to let the other person keep their own sense of happiness. I am here because I choose to, he is here because he chooses to. We are free to go, if we choose, or free to stay, if that's what we'd rather do.
That's what I think our "compatibility" is about - that we're both able to be ourselves whilst fitting into each other's lives.
And though small children can put a strain on any relationship, I think, for the work that is involved can sometimes be just... geesh f*ckin' christ, it's also important that we share our kids together and are able to enjoy them together.