Everyone seems to take the fact that their body works like a wonderful machine for granted....... until it doesn't.
The thing with backs is that, in my personal experience, you don't ever expect to cause permanent injury. I was just trying to plug in a cable in a server rack that I couldn't quite reach... I stretched and twisted, and the pop in my back didn't seem like a big deal. Turned out I'd damaged a disc and it's an injury that has plagued me off and on for years. I can't stand or walk for very long without minor pain.
Only permanent thing to do be done for it is back surgery (probably fusing the vertebrae), and my doctor assures me that back surgery will be worse than anything I've experienced so far. (Which includes picking up a napkin off the floor of a hotel and finding myself flat on the floor, unable to stand.)
Backs don't heal readily, and permanent damage is certainly a possibility. It doesn't help that my career has me sitting on my hind end all day.