For minimum disappointments, it is much safer to expect less from others. People will make promises to you and fail for good or bad reasons. They will assure you and renege, they may even be there cheering you and you will think they are happy for you, only to find out they intended that you fail.
Never trust someone 100% except maybe your parents. The more you expect and depend on others the greater your chances of disappointments.
Your best bet is to expect more from yourself, work hard to meet your self expectations, that way you will become a better person because you are inspiring yourself and subconsciously pushing yourself and your limits to greater heights.