Believe.

That is, believe in yourself, but don't always believe yourself. 

Bumper sticker wisdom advises, "Don't believe everything you think," and, while we shouldn't follow just any bumper sticker wisdom (I'm looking at you, "Honk if you love peace and quiet!"), I think this is some good, free advice.
The evidence-based therapeutic modality Cognitive Behavioral Therapy (CBT) focuses on the concept that we can feel better by first noticing--and then changing--our inaccurate thoughts and beliefs. Have you ever spent a few minutes just listening to the way you talk to yourself as you go about your day? What do you say to yourself? 
In the 1960's, psychiatrist Aaron Beck noticed that his patients had a running internal dialogue of emotion-filled thoughts, which he called "automatic thoughts." An example of an automatic thought might be, "I never get things right. Guess I'll never learn," or "He/she just yawned... I must be so boring." These thoughts would pop into Beck's patients' minds without their awareness. With help, though, Beck's patients could learn how to first pay attention to automatic thoughts and then to challenge them. Beck found that identifying these thoughts was instrumental in helping clients to solve their problems. Over time, behavioral techniques were introduced alongside these cognitive approaches, and CBT was born. 
This brings me to "Believe in yourself, but don't always believe yourself."
According to some estimates, we have up to 70,000 thoughts per day. By paying attention to at least some of them (for starters, the ones that scream the loudest), we can begin the process of changing our perceptions, our emotions, and our behaviors. The next time you find yourself thinking, "I'll never get this right!" try consciously restating that message. See how you feel when you instead tell yourself, "Every day, I learn a little more." This Ted Talk by David Burns, author of the classic work on CBT and depression Feeling Good: The New Mood Therapy, provides some additional insight into CBT and its benefits.