Recently I had a discussion with a friend who just started a new faculty position. There are both positives and negatives with his new situation. We discussed how it is easy for a few negatives to weigh upon us and we lose perspective of the bigger picture. This is particularly true for those of us who are more introspective and melancholy, and possibly perfectionists. No job is perfect. There will always be frustrations and disappointments.
Some of these issues are addressed in my post, Should I change jobs?
I also think some people loose perspective about positives. They have a success [whether finishing a Ph.D., getting a grant, or a paper in a luxury journal] and they start thinking they are entitled to all sorts of things [whether, a permanent job, large amounts of funding, a promotion, ....].
How can we keep things in perspective?
Talk to others about your situation.
Write a list of both positives and negatives.
Factor in how your personality distorts your objectivity.