User blog comment:DE-Note/What Determines the Strength of One's Aura?/@comment-11188061-20150529121159

In truth, to emphasis on the 'Purity of the soul' wouldn't make a lick of sense.

As you grow older, you'll understand that the so-called 'purity' is actually the ability to concentrate one's mind on a number of tasks. A child can easily focus on a few tasks at hand (because it is the only stuff they understand, or want to) and is less inclined to be distracted by voluntary indulgences. Their capacity of the mind is not overloaded and they do not know what it means to 'tire' or 'be lazy' - thus they can easily excel in the subjects they chose to focus on. This is why most 'heroes' in stories are teenagers - they are just at the age where their capacity of the mind is not overloaded yet, and unlike the younger kids have developed through many hardships a concrete ideology, belief or the way of life they want to be.

As we grow older we carry more responsibilities, and we get overloaded by so many tasks (and the details within needed to perfect the job) that it became literally impossible to excel at everything. We've learned to be lazy, learned to indulge in relaxation, learned to hone our efforts onto that one thing that we love and everything else is built for the sake of supporting that chosen path. We develop techniques to better organize our thoughts and segregate exactly how many portions of our heart on the overwhelming number of tasks that we have to complete.

Most don't succeed. Even geniuses will hit their own boundaries. Very few can retain the ability to define and complete those tasks with clear lines without having them all blur together in a mess despite timetables and schedules and account books and working plans. There are plenty people who have hit their limits who thought, "Oh, I'm getting older, hence I'm getting lousier day by day" or some other excuses that subconsciously weaken their will and live only within their comfort zones without ever getting out. This is especially enforced when adults suffer much harsher penalties for taking a risk and fail, which turns them into mere creatures of habit. When you're following a habit, you don't think. The mind automatically executes a number of patterns that's been practiced day by day to the point that the person don't need to think, and when you stop thinking you don't improve, and when you don't improve the only way to go is down, down, and down until you hit the absolute rock bottom.