This one is so true; the universe runs on a funny little thing called karma. You definitely get what you put out there and it's something I notice on a regular basis. When I'm having a bad day, my mood is automatically bad and then everything that day is BAD, but when I consciously try to be better by smiling at strangers, holding the door open for people, saying thank you and just being polite and nice, everything seems better. People reciprocate that and they are nice back.
So next time you're having a bad day and things are going from bad to worse, pause and take a deep breath. And smile at the next person you see.
Things will get better.