Math-related metaphors

Do many here have a list of favorite math-related metaphors?
There’s not a specifically-math-related section of this Forum, but mathematics can be considered a branch of philosophy, I believe.
Here’s a metaphor that I think kicks some donkey kong:
http://www.npr.org/sections/13.7/2010/07/23/128716508/the-universe-and-the-infinite-library
That is, the Library of Babel