How can an adult still hurt itself?

Was the question Mieke asked me this morning after learning that Matt tore his achilles tendon last night (he has been playing basketball again for about a month - yeah for sure, I said, playing is a great idea, the exercise will do you good). According to Mieke, being grown up should mean we are free from injury and she can't comprehend how on earth he did that, when she falls all the time and only ever has a scrape requiring a Shrek bandaid and a kiss. Quinn fell backwards off our couch he didn't even get hurt. Dad's heel is going to need a lot of kissing. And some surgery.