Mental strenght is just an idea. Strenght itself is a concept, not a thing, something we derive from strong acts. In the same way, use your mind and you'll be using up your strenght. If you are asking for books to give you that, if you think that this is what is lacking in you, then you are still hoping something else can change yourself and your life and not you. This hope and this excuse of self-improvement is the very material in which your cage is made, as it fuels you into thinking you have matters to solve before acting out and learning your lessons.
People can show you several different books, but you won't be able to tell them apart, because you'll be so engulfed in this delusion of your own mind that you'll consider it a help when a book reinforces your current beliefs, points to a method, reaffirms your life, and offers the solace of security, even more so when it criticizes you and hints to your flaws, so that you have something to mourn and an excuse to ignore action, keeping you within the enjoyment of not being ready.
It's such bad news that you are responsible for your own life.
