Essentially, all models are wrong, but some are useful.

George E. P. Box (1919-2013) Anglo-American statistician, quality scientist [George Edward Pelham Box]

Empirical Model Building and Response Surfaces (1987) [with N. R. Draper]

As written on p. 424; earlier in the book (p. 74), it is given as: "Remember that all models are wrong; the practical question is how wrong do they have to be to not be useful."