So the, IF you are in a depressed mood, you will be too depressed to solve problems, which in and of itself requires some form of optimism.
And please, by all means necessary, stay away from negative thoughts when problem solving. Is that like "I'm going to draw the cb off the 4 so I can position for the 5. BUT WAIT, I'll probably miss." In the game of pool, nothing solves negativity like pocketing well.