The limited capacity of the brain

I am about to graduate and while I was studying for the last advanced exams I often checked books with basic concepts of those subjects, to review notions or knowledge I did not remember well...even though I had studied hard.

This situation reminded me of a funny but significant passage in "A Study in Scarlet", the first book about Sherlock Holmes written by Conan Doyle.
In this passage Watson discovers that Holmes has no idea about the solar system, nor that Earth orbits the Sun.

The answer of the detective is fascinating:

"I consider that a man’s brain originally is like a little empty attic, and you have to stock it with 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 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."

(Drawing of Sidney Paget)

One often thinks that everything can be stored in our mind permanently and that our brain's capacity is infinite, but, as everybody realises at the end, it is not possible. But I don't want to forget about the solar system for this 😜