Proposal: Keep it simple. =P
Current dictionary definition states at the first meaning "a lamentable, dreadful, or fatal event or affair; calamity; disaster", that's pretty much what I see it being used as in general. It's something terrible, that is lamentable. (And lamentable kinda depends on the person's perception.)
So essentially that's completely removed from self-inflicted or deserving it or whatever.
Though, what ayase cites with that Renaissance bit seems to come from a British dictionary specifically. So BE/AE diffrence perhaps?
But if you remove the theatre and literary definitions there is also "the unfortunate aspect of something" and "a shocking or sad event; disaster".
I'm struggling to think of a good example, so this crappy one off the top of my head will have to do - Say a person is allergic to peanuts, and they are driven to suicide and choose to eat peanuts and die. Tragic, because they did that to themselves. Now say they accidentally ingest peanuts and die. Also tragic, because while they didn't even know it, they still did that to themselves. This is what I understand is meant by the term "a tragic accident". Now say someone else purposely feeds them peanuts in order to kill them. Not tragic, just murder, because the person had no knowledge or hand in their own demise. At least that's how I understood the term. Of course, I may just be totally wrong.
Then what about a lightning strucks down, when you were just out to bring out your trash. Self inflicted, because you just happened to be out at the time? Then would that also apply if someone runs amoks and kills people, self inflicted because they were unfortunately there at the time?
Though your distinction kind of reminds me of a TED talk from a woman working as a disaster relief worker. She was trying to convince people that death at the hand of a hurricane aren't just a natural disaster that befall you and that's just how it is. But that it's something that was foreseeable and avoidable, but goverment construction planning actively doesn't do. (Citing buildings done in dangerous regions or less greenery in poorer areas, causing those areas to heat up more and raise the chances of heat strokes.)
Not exactly the same and I also can't seem to find the talk anymore to check if she was talking about disasters or tragedies and how exactly, but her point to get across was essentially, that the tragedy/disaster is self-inflicted by humans themselves and nothing from a higher power or so.