Why do bad things happen?

For every action, there is an equal and opposite reaction. That's how things work. If there wasn't any bad, there wouldn't be any good. Bad things sometimes happen as a result of the decisions we make (see Free Will). For example, if someone chooses to eat a lot of junk food or smoke, it's likely that they will experience health problems. Other times, nature can go wrong which can cause disease. But whatever we do, we mustn't blame God when something does go wrong. Instead, we should be thankful and take comfort from the fact that whatever happens, if you are a good person you'll be fine. Death isn't the end. How we react to and deal with certain circumstances is a test of character too.