For me, nice means doing what's expected and being agreeable, and kind means being caring and helpful. For me, nice has a negative connotation of faking and trying, and kind has a positive connotation of genuineness. However, both nice and kind can be faked, can be done to please, can be goal-directed, and either one can be genuine. I can extend myself being nice or being kind. I was more into being nice when young, and am more kind now. You never know for sure from where someone is coming. I have often endeavored to make an interaction meaningful, sometimes out of being nice, sometimes out of being kind, sometimes trying, sometimes being sincere and genuine. What motivates me even when it's hard and inconvenient is sometimes wanting to be kind, sometimes wanting to be nice, sometimes wanting to impress, sometimes a sense of responsibility, sometimes simply being me, and probably more.