First of all, it’s so much more fun when we’re not pressuring ourselves to do more than what feels right.
Second, it helps us learn self-regulation, how we can modify the intensity of our own experience by varying our movements and breath.
And third, learning to listen to the signals of our body is part of what keeps us safe in the world. The New York Times made this point strongly in an article this week entitled How Yoga Can Wreck Your Body.
I don’t really know why people try to push themselves into positions (or places) that don’t feel good. Is there some kind of rule that says you have to? If someone, somewhere, made that rule and is trying to put that on you – just give your attention to your inner teacher instead.