I think there's more to CBT than simply thinking positively, it's more about finding negative thinking patterns then thinking more "realistically", for example "I'm a complete failure" becomes "I'm a person trying my best and have good and bad points" and also realising there's no evidence to suggest the "I'm a failure" statement. Personally it doesn't work for me, I'm happy punishing myself and treating myself badly and no amount of thinking more "realistically" helps. As I said for me it's a problem that I know my negative thinking patterns and behaviours but struggle enormously to change them or even want to change them. I did find 15 years ago that when I first learnt CBT techniques it did help but it slowly became a battle in my head as to what we're negative thoughts and what weren't. That in itself is tiring and depressing.