Being nice often means being inauthentic. It can be a form of control -- attempting to control how the other person feels about you or how they respond to you.
We all have a wounded self -- our ego -- that we developed as we were growing up, to protect us from pain. Our wounded self becomes activated when we get scared -- scared of rejection, of engulfment, of being hurt.
You can read every diet book and try every weight-loss drug and every new diet, but if you don't learn to manage your painful feelings in ways that don't cause even more pain, you will not lose weight or keep weight off.
"Isn't withdrawing from conflict just running away?" you might ask. Yes, it is. But there is a huge difference between withdrawing and disengaging. The difference is about your intention.