Emotion is a great media for influencing the sub-conscious.
Therefore emotions + a belief gets easily transported into the
sub-conscious.
Repetition strengthens the belief.
So when you are flustred and think you have two left feet
repeatedly, you will expect to be clumsy, and will really be
clumsy. Or any other characteristics you can think of.
You think you
are clumsy, or whatever, and you are. Remember, you can just as
well think good of yourself. Infuse that thoughts with emotions
repeatedly and get it into your sub-conscious.
Truthfully think back about your thoughts and categorise them.
Are they happy or moody, and match them against your character.
But bear in mind, years of negative thoughts cannot be erased by
a few minutes of positive thinking. You got to persist in the
good habit till it becomes second nature. You will dismiss the
negatives, and focus on the positives this time.
Dwell on the good things that you have, and be happy thinking
about it.
Unfortunately great effort is required, for we will always face
"attacks" ( like criticism, insults, humiliation, failures
and also blunders) that will seek to undermine the
effort.
Count your blessings, always.
Happily.
Hmmm, you accurately described what i was in the past
it took me years to walk out of it