Negative thinking
I know some people who used to complain that life is too unfair towards them; they can not achieve anything as there is not any opportunity/desire/goals/understanding/support. The worse thing is that this way of thinking is becoming dominant after the long and stubborn repeating "I am a loser. And what could I do?". It is twice awful that such model is suggested to the children who used to bring it into their families when they grow adult.
If you catch yourself that you are thinking in a negative way, shake yourself and tell something opposite. When you feel that you start negative reflections again, try to change the activity, remember a good and easy moment of your life, imagine what you felt that time. It allows your nervous system to relax and concentrate on the positive impressions only.
Some people are really afraid to be mistaken and blamed for that. It proves lack of self-confidence. Just remember that you are not the first one who make mistake doing something and nobody would kill you for your fault.
Speaking about the psychological reasons of negative thinking, it is the result of incapability of your ideal to correspond to the reality. At least you are not the worse person in the world. You make mistakes, you feel sick and tired sometimes, but you are not worthy to be humiliated by yourself.