A successful tool is one that was used to do something undreamed of by its author.

(Other Authors and Sources)

S. C. Johnson

Attributed to both Samuel Curtis Johnson, Sr. (1833-1919), businessman and founder of S. C. Johnson Wax, and (more likely) to Stephan C. Johnson, contemporary computer scientist. In the latter case, it is often written as "A successful [software] tool is ..."