“You see,” he explained, “I consider that a man’s brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things, so that he has a difficulty in laying his hands upon it. Now the skillful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work, but of these he has a large assortment, and all in the most perfect order. It is a mistake to think that that little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.”
I think, this concept may be wrong if we accept the fact that normally the conscious part of the brain utilizes only 10-13% of the neurons. But this theory has its own charms and can explain the focusing ability of a person and the power of deduction. As in you don't know so much that you find loopholes in almost every theory while you know enough to form theories of your own. Given the internets, it becomes even more important to have a mechanism through which one can sift through reams of information among which only few of the data points may be useful.