Arthur Conan Doyle. A study in scarlet (№ 428439)

... in my opinion, the human brain is originally a small empty attic, which you have to furnish at your own discretion. The fool drags there any piece of wood that comes across on the way, so the knowledge that he really may need is pushed out of there or turns out to be cluttered with so many unnecessary things that it is simply impossible to get it if necessary. Homo sapiens are very selective about what they place in their intellectual attic. He will not fill it with anything but the tools needed to do his job, but he has an extremely rich assortment of them, and he keeps them in perfect order. It is a mistake to believe that this small room has elastic walls and can stretch to any size. Therefore, the moment inevitably comes when, in order to add any new knowledge, one has to throw out of the head some of the previously acquired knowledge.