I don’t want to argue here. It is just a matter of perspective. But speaking for myself, trading is not a gamble for me.
The purpose of understanding trading psychology is to avoid emotional trading. And managing our emotions while trading is very important in my opinion. And I personally think that no book will ever be useless as long as one can learn something new from them.
I’ve read Trading in the Zone by Mark Douglas, I really liked it, here is another good one I read - The Mental Game of Trading by Jared Tendler