I think what I did was to realize that no one is going to always meet my expectations. That to live like that means always being disappointed therefore. That my expectations only reflect what I think and would say or do, and cannot reflect what someone may think, say or do. That to have expectations is a form of exerting control over others. That it's better to have no expectations and be pleasantly surprised when good things happen, rather than be disappointed and frustrated all the time.
Those were sufficient reasons for me to see the wisdom in letting it go.
