Every person has his own capabilities, his own nature and way to do things. We tend to expect a lot from some persons, and, naturally, when we don't get what we expect, we are disappointed.
In 'Bhagwad Gita', it is said that we should just do our work, and should not worry about the result. How many people actually follow this? We expect good results everytime whatever we do. If we just leave to God, we would be much happier. Likewise, what others think, or whatever they do, is not in our control.
If we expect none or less from people, we will not be sad or disappointed, whatever they do. We will be happy if we receive something good from them
So, my dear friends, don't expect, but accept!