Bad things don't just happen to good people. They happen to everyone, not just the good. The reason why? Its life. The only thing is, we must decide whether or not we want to get back up after those bad things and hard times.
Bad things that happen is what builds our strength and character as a individual. Life is what you make it. You can accept things and grow as a person or you can be bitter, pitiful and miserable blaming others for misfortunes.
THINGS happen to people. Some of the things are good, some are bad. Some of the people are good, some are bad. If you want to be successful in life the trick is to capitalise on the good things, and handle the bad things to the very best of your ability.
I used to work night shift with a guy called Bomber Brown and we played euchre when it was quiet. The stake was one lottery ticket a week. We were very level in ability but Bomber played his bad cards a little better than I did and, once in a while, he'd win a hand that he should have lost. The result was that he never one had to buy a ticket. I bought them all.
That's the secret. Anybody can play well with good cards; it's how you play the bad cards that determines your quality of life.
What is "bad" outside of the definitions we as sentient beings give to occurrences at one end of the good things/bad things scale? Why do things happen to people at that end? Because they happen all over that scale. Sometimes, it's at the "bad" end.
One of my ESL student asked me this question a few days ago. I asked her; doesn't the rain fall on everyone, the just and the unjust? In short, bad things happen to everyone, it's just more noticeable on 'good' people because of the life they lead (e.g like my student). Just forget for one minute that people are beyond good and bad and that we are in sense among the plants and animals that inhabit the earth. When a fox catches a rabbit and eats it, do you think this solely good or bad? As we see it, it's obviously bad for the rabbit, but good for the fox. What did the rabbit do to deserve the bad and what did the fox do to deserve the good. It just is! ;) Get my point? :P