If you’re a long-distance runner who trains hard every day, your knees are your weak point. Every time your feet hit the ground when you run, it’s a shock equivalent to three times your weight, and this repeats itself perhaps over ten thousand times a day…
…If you think of this (and I admit it’s something I don’t usually think about), it would seem strange if you didn’t have a problem with your knees. You have to except the knees to want to complain sometimes, to come up with a comment like,
“Huffing and puffing down the road’s all well and good, but how about paying attention to me every once in a while?
Remember, if we go out on you, we can’t be replaced.”
Haruki Murakami, What I talk about when I talk about running, A Memoir, 2009, p. 127.