The feedback loops on attitude are incredible.
When you're in a bad mood, cynical, and hostile, you put people off -- and it justifies that attitude, because people will react poorly to you, and top-notch people won't want to be around you.
When you're happy, complimentary, jubilant, people want to be around you and even do random nice things for you -- I was just in a particularly celebratory mood going to a cafe, greeted and complimented the owner, and she sent some free watermelon over.
It's funny - the free watermelon would help a lot more during bad days to reinvigorate hope and good feelings, but it doesn't work like that. When you're going great internally, that's when you get random great little (and big) external things.