When people think about happiness, they usually think about being happy for positive things that occur. Rabbi Simcha Zissel of Kelm, (1824-1898) wrote to his students to appreciate what didn't happen. He commented on a puzzling custom that he saw. When a shirt would fall from a clothesline down into the dirt, some people would say, "I am grateful that I wasn't in that shirt." It sort of makes you want to smile, doesn't it?
He explained that people play games and listen to music in order to enjoy life. Developing the habit of being grateful for all the wrong things that didn't occur in your life will add to your daily dose of enjoyment.
When you learn to appreciate what didn't happen, it's mind- boggling how many bad things don't happen to you in one day. I've told some people to make a daily list of ten bad things that didn't happen to them. Some find this unpleasant. And for them there are other paths to appreciation.
(From Rabbi Pliskin's "Happiness",p.134)