Simply stated: the right amount. From a grocery store transaction standpoint, there is one clear answer. It is neither too much nor too little. It is a balance; a FIT state. When a clerk counts back your change, there are certain bounding elements that are external to the desires of either party. Natural laws of fairness dictate that neither party get the better of the other.
However, this is not as clear cut or universal with regards to person change. Change, in both senses, merely indicates a difference between one thing and another. In the grocery store, your change is the difference between what you owed and what you gave (a $20 bill, say). In life, your change is the difference between who you are now, and who you become through education and experience. That education—or more precisely, what you gain from it—is the difference.
While I don't believe it is possible to be over-educated in general—especially when the education is broad—it is possible to take too many things to heart. In this way, an individual can needlessly toil to change himself in areas where the benefits of such a change are not worth the cost. Each individual is different from every other individual, of course, so this process must necessarily be tailored to suit each.
For example, a person who is an extrovert might find it difficult to focus on a lecture, daydreaming of more action-centered activities. They can't wait to get out in the field—for sports, sales calls, parties, or networking. They struggle to follow endless charts and graphs, even those which accurately depict the current situation and ought to equip them of their next move. Should they be trained in the art of memorizing these graphs, or should they simply be allowed to learn from trial and error?
In the opposite case—and, I believe, a more widespread problem—a person who is an introvert finds it difficult to focus at a party, desperately planning an escape. They can't wait to get away from the action—to recover themselves; to collect, categorize, and formulate an understanding. They struggle to take in the endless tidbits of information, when the real focus is merely to meet a great many people. Should they be trained in the art of networking, or should they simply be allowed the time to fully absorb each interaction?
Ultimately, the answer to the question depends upon and understanding of where you are right now, and where you want to be at some defined point in the future. Note that while the span of time between now and a dated goal varies by the goal and the person, for everyone who has a goal it is essential to commit to the date. When you set a date for well-defined goal, and begin to understand where you are right now, you can plot a course to change.
This too, varies from a learn-by-doing process to a carefully composed plan. Nevertheless, the main lesson here is that when we understand our strengths, we must utilize those strengths. For every strength in our character, we have correlating weakness. Never attempt to reach a goal by changing your inherent weaknesses. While this can be done, it is rarely worth it. Weaknesses should not be ignored—they are real obstacles—but for those boulders whose destruction risks the destruction of a correlating strength—again, it's not worth dying over.