A library grows useful through the books people can find, not merely the books it owns.

Owning something is not the same as offering it. A collection is only as large as the part an ordinary person can locate on an ordinary day without asking twice, and the rest is storage. Catalogues, signs and somebody to ask are not administrative extras. They are the difference between a room full of books and a library.

The same holds for what you keep at work or at home: the file nobody can find, the knowledge that lives only in your head. Spend an hour making one of those findable by someone else. It multiplies what you already have without adding to it.