As the annulus weakens, at some point you may lift something or bend in such a way that you cause too much pressure across the disc. The weakened disc ruptures while you are doing something that five years earlier would not have caused a problem. Such is the aging process of the spine.
My wife has a genetic disorder that (among many other things) causes her spine to herniate at the drop of a hat. She's had to have emergency surgery multiple times.
About a year and a half ago, a neurosurgeon was operating on her and came to talk to me and my mom who were waiting. She was extremely excited, in that like "academic who just saw something new" kind of way, because my wife had the third biggest herniation she'd ever seen, and the largest in a patient under 70 (my wife was 34 at the time). She asked if it would be OK if she invited a professor from the local university and a couple of his grad students to come look at it.
Oh wow. Congrats... I guess? Glad that your wife has access to good care for that condition.
I've been in the ER for something that... well I won't say, but it was of interest to the attending folks. Next thing I knew, there were two grad students in tow, eager to learn stuff that you only usually see in a textbook. I recall feeling strangely proud, and more proud than embarrassed (oddly enough). It was a weird experience.
Also the surgeries often have to be done from the front, so doctors have to put organs out of the way, operate the spine, put everything back. It's really scary. Everytime I think of it I start sitting a little more upright.
The spondylolisthesis (listhesis) one isn't quite accurate - it should be the whole spine above the joint in question shifted forward. You don't really see just one vertebral body sticking out like that.
Fun fact: discs can herniate multiple times even after you've shrunk half an inch in height and think all the cream has been squeezed out from between the cookies.