The "maybe you should give up mountain biking" comments are annoying.
Yeah, that's gross.
Two of my most chronic issues have been wrists and shoulders. The shoulders are definitely linked to office desk posture; the wrists - come on - I'm a software engineer. And yet no one has ever suggested I should quit my desk job and do something more dynamic. (I just reminded myself to sit up straighter, LOL!) My neck and shoulders were at their best when I was recovering from surgery - I worked exclusively in a recliner. I don't think I'll be able to convince any office to put a recliner at my desk ...
The ACL process has had, and continues to have, an exponentially bigger impact on my life than any other injury. It did make me rethink some things, but that rethinking led to me realizing that while some activities weren't that important to me (hint: ones that I didn't do that often), others absolutely are worth the risk. I was surprised to find that mentally, I'm right back in the game with skiing and mountain biking. Unfortunately, my knee is still not with the program. So that was a surprise.
On the other hand, I can see where eventually injuries could take enough of a toll to make me think, "Okay, enough!" I love intense sports where there is a risk of injury, because they help me focus and I love the rush of doing something scary (just the right amount of scary - I have to know it's within my abilities) and succeeding. It's not surprising that doing that sort of thing can occasionally cause injury.
And yes, I know plenty of people who've gotten hurt just walking along, doing something normal. It would be interesting to compare the rate of mountain biking or skiing injuries to car related injuries *by number of hours*.
Weirdly, such a major injury can have a silver lining (and I always do look for a silver lining). All the posterior chain work I did for rehab has given me a much more efficient pedal stroke. I'm not talking speed per se - but before the injury, my quads would get sore pretty much as soon as I started riding. I just bulled through. These days, that doesn't happen on the same trails, and sometimes it's my hamstrings that are sore after riding. (PS - this is with flats!)