When we focus on one particular area, we tend to "defocus" on other areas, some of which could be extremely important: family, happiness, the future. But by focusing on one particular area, it increases the chance that we'll have success in that area.
Like a kid using a magnifying glass to burn ants on the sidewalk, or like a nail being driven home by a hammer, focusing our energy on one single area gives us power and energy that we can get no other way. It's a useful mechanism to create change in our lives. Many people use an alteration of this technique, maintaining extreme focus for enough time to accomplish change, and then moving the focus to a new challenge to overcome.
MORAL:
Whatever way you work on it, extreme focus is an important technique to accomplish change in our lives -- as long as we don't go overboard to the detriment of the remainder of areas that we must include in order to achieve true happiness.