Tragedy.

1) Tragedy is an event that causes great suffering. Everyone experiences their own sort of tragedy in their life time. It is what you take from the tragedy and how it shapes you as a person that is important.

2) To his loved ones, for example, Morrie's death is a tragedy. They suffer greatly from his absence. They experience true hurt through their loss. Morrie taught and gave to all of them. His life was a gift to them. And now that he no longer has life, they miss his presence in their lives.
To Morrie, his death is not a tragedy. He is thankful that he has time to give back more before he goes. He explains this to Mitch and says that not everyone is as lucky as he is, because he has a chance to make things right be fore he dies. Some people continue through their average lives, going day to day, and then one one of those average days they die. There lives are left incomplete. So Morrie fills his day to day with love and teaching, so that his life will feel complete.

3) Perhaps tragedy isn't necessarily a loss. Maybe its the feeling that you didn't know what you had. This leaves us puzzled and insufficient. This is what we translate into the feeling that comes after tragedy strikes; sadness. We mourn for the things we had yet to know. Not only does this feeling occur with death, it occurs with any misfortune. With every choice we make there is something to gain, and something to lose. For the things we cannot control, there is the simple explanation that that's how life goes.

4) Is a love lost a tragedy?
When something or someone leaves our lives, we think of it as our loss; our misfortune. But it is only when we lose something that we realize its importance. And if you are lucky, you are able to realize this soon enough to salvage the love that was lost.