Among the many purposes of mantra, japa, affirmations, or prayer, is to keep the mind under control. When left unattended, the mind can travel to many random thoughts, at the same time. It is guaranteed that an unattended mind cannot be fixed upon positive thoughts all the time. For some of us, the mind is programmed to default to negative thoughts automatically.
This can be a result of past experience, conditioning, heredity, or, possibly, this is an organic problem. In the case of an organic problem, professional help should be sought. Yoga therapy, or Yoga sessions, will still help, but a competent psychiatrist is still needed. If the source of low self-esteem is in your past, you may be able to address it through self-analysis, meditation, or mindfulness. If it is too much to handle alone, a trusted friend, mentor, Guru, or counselor, may help you bury the past. Meditation sessions should be spent pondering a positive solution.
Meditation time should never be spent on negative thoughts, or rehashing past mistakes. We cannot change the past, and we must realize what parts of our lives can realistically be controlled. There are situations in life, which are far beyond our control, and we have to come to a realization about the limits of our control. We are responsible for our actions. Therefore, forgiving oneself for past mistakes is a difficult task for most of us.
Yet, if we do not forgive ourselves, we prevent our own happiness. Self-worth and happiness must start from within. We must accept the past, our friends, and our family, as they are. This is the practice of Santosha: To be content with life as it is. We cannot change the past, and we will only frustrate ourselves if we try to change people, but we can change our own thinking process for the best.
Look at mistakes only for their educational value. All of us make mistakes, because we are human, but with every mistake, there is also a hidden opportunity. This is what separates successful people from those who spend their lives dwelling on the past. How many times have we heard a Yoga teacher say "Be present for practice." or "Live in the moment," Many Yoga students practice Asana, but how many are really present for their practice, As we roll the Yoga mat up, and go about our lives, we should be present for life. This is a state of "mindfulness" or non-judgmental awareness. If you really want to raise your self-worth, stop judging yourself.