One can see clearly some ambivalence in Dirac's attitudes... On the one hand, he has repeated many, many times his conviction that beauty in the fundamental equations of physics has priority... On the other hand... we see Dirac deeply involved with approximate calculations whose only purpose was to obtain an answer which the experimenters could rely upon.

R. H. Dalitz, Another side to Paul Dirac, in Paul Adrien Maurice Dirac (Cambridge University, Cambridge, 1987) Chapter 10.