This is also a myth. As someone who has trained a lot of regular people, some are incredibly tight, to the point that they will not be able to perform movement

This is also a myth. As someone who has trained a lot of regular people, some are incredibly tight, to the point that they will not be able to perform movements correctly without stretching prior to the workout. Sure, they don't stretch right off the bat--a 5-10 "active warmup" is great--but sometimes stretching before a workout is necessary. It's not like we're dealing with elite athletes here; no one on HN is going for an 800 lb squat. And even in that realm, Jim Wendler of EliteFTS.com recommends static stretching prior to workouts. Even better than stretching or at least as good, which I don't think anyone has mentioned, is myofascial release. Basically it's a self massage with a lacrosse ball or a foam roller. Mix a little bit of this soft-tissue work into your regular stretching and you'll see huge results.