I came here to post The Inner Game of Tennis and was pleasantly surprised to see it in the top comment.

The book is only tangentially related to tennis - the real meat of the book is about how to adopt useful mentalities which will help you succeed at a variety of things. It's an extremely easy read and can be finished casually in a few days.

A great book which made me question some of my most deeply held beliefs about learning.

Back when I was still a student (of music), I read The Inner Game of Tennis and found it to be incredibly useful!

I also recommend it.