happiness is pleasant thinking
Happiness is a state of mind in which our thinking is pleasant a good share of the time.
- Dr. John A. Schindler
The feelings we feel are based in the nature of our thoughts. It does not have to be the content of the thought but rather it is the context of the thought.
We can think about negative and bad things but in a compassionate or empowering way. The same way we can think about great things in a pessimistic way. That's why the good old advice of "think positive" does not apply that simply. It is the context of the thought that matters and that determines our feelings.