If you could go back in time and tell yourself to read a specific book/text/guide/tutorial at the beginning of your career as a gis-developer, which book would it be?
I expect this list to be varied and to cover a wide range of things.
This same question was once asked at stackoverflow for programming topics, and it has been considered by some as "one of the most important question ever asked on stackoverflow". So I decided to bring this question to serve our needs here at gis.stackexchange.