Shereshevsky, in his maladroitly-titled book “The Soviet Chess Conveyor”, advises the student to study the classics. This is advice with which I heartily concur.
It’s only when he goes on to make an exception for all but a very few masters before Botvinnik I have the timerity to disagree with the famous chess trainer.

“The importance of opening theory is grossly overestimated. Obviously, the knowledge of opening moves comes in handy when setting up a chess game, but this knowledge alone does not bring universal happiness. After this, you still have to play chess, and for that, other things will crop up.” ~ Herman Grooten (Dutch trainer of, among [...]