There is usually a gap between ourselves and our ideal self, AKA, the self that we want to become, and when we do things that hinder our path to this self, in the form of submitting to temptation than to the desired advancement of this path, we can often feel very disappointed in ourselves, knowing that we could’ve been closer to the ideal self than we currently are.
It’s a possible reason as to why some of us may criticize ourselves harshly. We know we could’ve been somewhere else in life — somewhere better — but due to our own weakness we have failed in the attempt of advancing, which may also result in the decreasing of our self-worth.
Should we overcome short-term temptations in favor of long-term advancements, we may criticize ourselves less harshly. In many cases, short-term temptations are not worthy in contrast to our long-term ambitions.
Another solution is to try to be more realistic and more forgiving. Should we find ourselves submitted to short-term temptations that hinder our progress to our ideal self, we should ask ourselves whether or not being harsh upon ourselves is really worth our time and energies. Even if we ultimately won’t reach our ideal selves, something which is a possibility, we can still enjoy and feel good about ourselves even if we believe we can be in a better position in life.
And indeed, one of the benefits of a more-ascetic life and mindset is the ability to find comfort and satisfaction in the present moment and in what is presently available, rather than making us suffer over what we don't have yet or have failed to achieve thus far.
Yet another solution is to bring our ideal self into proportions, because the further you’ll put your ideal self beyond the sphere of realism, the more likely you’ll suffer for not being able to reach it regardless of your endeavors.