Bad stuff happens to good people and good stuff happens to bad people. Also, good happens to the good and bad happens to the bad. It's called life. We all react to events in a different way and sometimes we are changed. Sometimes we remain unchanged. Again, it's called life. Personality, education, upbringing, friends/peers, immediate family, economic situation, etc. can affect one's reaction to tragedy.
I don't believe that it is appropriate to say that generally tragedy makes people stronger. There are many factors that play into how someone handles tragedy. If tragedy strikes when a person is already down, it can certainly spiral them further downward, and if not, it may take a lot of processing time to reach a point when they personally feel strengthened.
Tragedy involves a certain period of mourning for the individual effected. As a matter of fact, there are several steps for an individual that seems to be pertinent in order to regain a normal thought pattern after a tragedy, regardless of the details. An example of the thought I would like to convey is that the same tragedy has different effects among different people and generally includes how personal the tragedy is.
In any event, the word itself does not indicate there are/have been actions of good favor which could make people stronger.
Tragedy does not make a person stronger, because the person is bent and broken while they deal with their terrible loss. Rather, tragedy makes a person fearful. They see what is bad in the world. they see what the person needs to do in order to avoid pain in the future.