There is a whole section of the Hayee Moharan about the idea "לא להתעקש על שום דבר" ("not to be stubborn about anything.") I noticed that one of the examples he brings there is about sleep. That is by trying to force oneself to go to sleep, that is exactly what causes sleep to evade him. And there are other examples there.
But that is not to say that there are not some things that one needs to be ("makpid") stubborn about. But that one ought to choose one's battles wisely.
[You could apply this to learning also. By being overly stubborn about getting the details perfectly, one can lose the big picture. I mean to refer here to the Conversations of Rav Nahman Conversation 76 where he discusses the importance of learning fast--saying the word and going on until the end of the book and only then to review. It is implicit in this that he is suggesting not to insist on understanding all the details. And in fact I found this method helpful in my Physics courses at NYU.]
