momentum of growing up

We grow into our roles, not the other way around. You need to fake it until you make it as they say. This is more or less a mathematical necessity since titles are discretely compartmentalised while self-improvement is a continuous process. In other words, a healthy, developing ego is always in a state of pretension. (While rational ones draw confidence from past establishments and competencies, delusional ones draw hope straight from religion and astrology.)

All the great figures of history were to a certain extent self-delusional. They either constantly underestimated their capacity for achieving great things, or thought they were above everyone else. A spring oscillates only when it is pulled in either one of the directions. People who are negatively self-delusional tell themselves "I need to do better than this." People who are positively self-delusional tell themselves "I can do better than this." In either case there is some momentum. A person who is fully aware of his limitations will be utterly incapable of taking the necessary steps to improve himself. He will never have a chance to discover the fact that his limitations are partly dependent on how much he is daring push them.

There is also the issue of building a momentum. Say your top potential is X. You will reach X faster if you aim for 2X rather than X. In other words, it can be optimal to overshoot a little more to gain speed. Of course, this can easily turn into a dangerous exercise and steer you into the territory of delusions.

P.S. You may also enjoy reading the old blog post Momentum of Aging.