Just like most parts of your body, your knees are a part that you take for granted until they decide to rebel against you.
As a child I did the most horrific things to my body. A memory that came back to me recently was climbing out of the window of the second floor bathroom at my Grandmother's farmhouse onto the roof, and jumping off for fun. We're talking about ten or twelve feet in the air, leaping outwards to land about ten feet away - feet firmly on the ground. The force I must have been exerting onto my knees is enough to make me wince these 22+ years later. I can't even remember having some sort of superhero fetish at the time, I just liked to jump.
Then you have all the other childhood experiences that would cripple an adult for life. Wiping out on my BMX bike while peddling full-out to jump some makeshift ramp. Randomly falling out of trees...including one forty foot plunge in Pefferlaw (I'll discuss that separately). As a teenager I mastered the pratfall on stage, but not until I practiced injuring myself in untold ways by doing badly choreographed flips and such. Now that's suffering for your art.
Over the last few years I have paid for my unwise machoism. My knees are pretty much sore and inflamed all the time. My love of running, skiing, hiking and baseball have all been put on the backburner; perhaps permanently. I even had to use a pillow so that I could get down on one knee to propose to my wife. I regret not having strong knees every single day, though have learned to live with my condition.
Everything is hindsight and time-travel hasn't been invented yet (or is a physics impossibility), so obviously I can't go back to smack some sense into myself as a kid. But I can be prepared to put the fear of god into my own kids if I catch them doing the kind of stuff I did. "You wanna walk like daddy? Huh!? I knew you didn't". That hopefully should be enough to make 'em think twice before they try their own death-defying leaps. Mind you, kids are naturally inquisitive by nature to the point of being downright suicidal, so they'll probably try anyway when I'm not looking.
Think I'll install parachutes into all their clothing.....