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.
 Arthur Conan Doyle, A Study in Scarlet (1887). copy citation

edit
Author Arthur Conan Doyle
Source A Study in Scarlet
Topic knowledge memory usefulness
Date 1887
Language English
Reference
Note
Weblink http://www.gutenberg.org/files/244/244-h/244-h.htm

Context

“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.»
«But the Solar System!» I protested.
«What the deuce is it to me?» he interrupted impatiently; «you say that we go round the sun. If we went round the moon it would not make a pennyworth of difference to me or to my work.»” source

Meaning and analysis

write a note
report