Happiness consists in activity. It is a running stream, not a stagnant pool-Oliver Wendall Holmes
This is certainly true for me. I can get depressed so easy when I have too much time on my hands. If something is bothering me, unless I stay busy, it will consume me. When you keep busy, your mind keeps busy, which leaves less time to ponder on the thing that is bothersome. So, next time you are feeling blue, make a point of doing an activity such as reading, walking, crafting, etc. It might not solve the problem, but it will put you in a better frame of mind, and who knows, sometimes it will give you a new perspective of the problem, which could lead to solving it.