Quote about trying before seeing

Question

Which book says, probably in its preface, that when you see a theorem in a math book, you should make a serious attempt to prove it before looking at the book’s proof? Thanks.

I know a similar quote that says when you are solving an exercise, you should never look at the solution, because solving a difficult problem brings you the greatest satisfaction.

Also, Bellman said, if you can’t solve a problem, you should treat it like a research problem.

Answer 1

Jeffrey Stopple wrote on page xiii of A Primer of Analytic Number Theory:

Most [exercises] have solutions in the back, but you should at least make a serious attempt before reading the solution.