“Whether you think you can, or you think you can't--you're right.” — https://quoteinvestigator.com/2015/02/03/you-can/
An effective form of 'treatment' for depression/anxiety is to recognize that negative feels often don't come first, but rather we are doing actions that cause them, so you should do the positive things and this will reduce one's negative emotions:
* https://www.goodreads.com/book/show/54930681-feeling-great