Be more realistic rather than optimistic.

Recognize your limits.
Overconfidence can cause unreal expectations and make us more vulnerable to disappointment. How well do you know what you don't know? Don't let your ego determine what you should do.

Focus on what can go wrong and the consequences.
Establish some margin of safety in decisions. Know how you will handle things if they go wrong. Surprises occur in many unlikely ways. Ask yourself: How can I be wrong? Who can tell me if I'm wrong?

Consider people's accomplishments and past behavior over a long period rather than first impressions.
Since people leave track records in life, an individual's paper record is often predictive of future performance and behavior.

Remember that successes draw far more attention than failures when comparing records or performances.