You see, 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 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 difficulty in laying his hands upon it.

Now the skilful 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.

-- Sir Arthur Conan Doyle, "A Study in Scarlet"