In his inaugural professorial lecture at Cambridge, William Bateson, one of the fathers of Mendelian genetics, admonished students of the new science:

 If I may throw out a word of counsel to beginners, it is: Treasure your exceptions! … Keep them always uncovered and in sight. Exceptions are like the rough brickwork of a growing building which tells that there is more to come and shows where the next construction is to be. (Bateson, 1908) 

William Bateson dixit (H.G. Spencer & J.B. Wolf, 

Genomic imprinting: theories and data, Heredity, 2014)