One of the most underrated attributes of a leader is his or her ability to manage expectations. This extends to personal, team and projects.
I learned this lesson early on. I distinctly remember posing this scenario to Dr. Henry Cloud in a class he was teaching. I asked, "How do you manage expectations so you don't end up being disappointed?"
His answer went something like this...
"A lot of times we have our own expectations that are best case scenario or idealistic and there's nowhere for you to go except down. I'm not saying lower your expectations, but think more at a realistic level so there's at least some room to be happily surprised."
I have high expectations and I don't have any intention of changing that. What I have changed is forcing my expectations on others or situations where I don't have much control over the outcome. For example, if I am leading a team I will set the standard high and expect my team to meet them, but if they don't I adjust. Anytime your expectations include another person, be prepared for a variety of outcomes.
When your expectations are too high, it's like putting someone on a pedestal...the only way they can go is down. People are going to let you down. That's not being pessimistic, that's a fact. It doesn't mean you don't put your faith in others, it just means we're all human and we make mistakes.