Here’s an interesting quote from Charles Haanel:

“Attention or concentration is probably; the most important essential in the development of mind culture. The possibilities of attention when properly directed are so startling that they would hardly appear credible to the uninitiated. The cultivation of attention is the distinguishing characteristic of every successful man or woman, and is the very highest personal accomplishment which can be acquired.

The power of attention can be more readily understood by comparing it with a magnifying glass in which the rays of sunlight are focused; they possess no particular strength as long as the glass is moved about and the rays directed from one place to another; but let the glass be held perfectly still and let the rays be focused on one spot for any length of time, the effect will become immediately apparent.

So with the power of thought; let power be dissipated by scattering the thought from one object to another, and no result is apparent; but focus this power through attention or concentration on any single purpose for any length of time and nothing becomes impossible.

A very simple remedy for a very complex situation, some will say. All right, try it, you who have had no experience in concentrating the thought on a definite purpose or object. Choose any single object and concentrate your attention on it for a definite purpose for even ten minutes; you cannot do it; the mind will wander a dozen times and it will be necessary to bring it back to the original purpose, and each time the effect will have been lost and at the end of the ten minutes nothing will have been gained, because you have not been able to hold your thought steadily to the purpose.

It is, however, through attention that you will finally be able to overcome obstacles of any kind that appear in your path onward and upward, and the only way to acquire this wonderful power is by practice — practice makes perfect, in this as in anything else.”