Coming back from mission I realized that we place our emotional stability in things that are not stable at all. For me, it was my friends, if a friend was there for me and we were doing things together then I was on top of the world, but if a friend lets me down I would be really bleak about life.
If we truly put our efforts into making God pleased with us then we will never be disappointed again because he will never let us down. putting our trust in the arm of flesh, which includes ourselves, is always going to be a letdown.