It's always good when we get a lasting lesson without any major harm. I don't know if you have ever worked somewhere that they had a professional safety audit done. That can be a real eye opener. Chances are they would have seen that piece of mdf and said put it away or dispose of it. When you look at your shop the way one of them would you start to see a lot of things that could be improved on.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.