Opposing Forces

Recently I have been thinking a lot about how to balance out optimism and disappointment. I would consider myself a fairly optimistic person who tends to expect the best from myself and everyone around me. It takes repetitive offenses to really make me expect the worst from someone. But I've also noticed that I tend to stumble across disappointment frequently when people don't live up to my expectations or ideals. How do I balance out being optimistic about people and opportunities without then having the disappointment when things don't turn out? I don't feel like I should automatically have lower expectations. Maybe I need a better way to deal with disappointment. Food for my thoughts at least.