Gregor Maehle changed the sentence from "no gain, no pain", into "no discomfort, no gain" in his latest book "Ashtanga yoga - the intermediate series". But something must be felt, otherwise nothing happens.
My tolerance to bear the stretching discomfort is not every day the same. Sometimes I can even enjoy it. Sometimes it is full of relish, but not always. However it is, it is good to go on with the practice. The longer I practice the closer I can come to the point where the discomfort turns into pain. This is the point where it is good advice to stop and to relax while remaining in the pose.
I can imagine that when the body is really soft and flexible one day in the far future a feeling can appear as if the body is not existent when practicing asanas, but till then a bit of aua means that the body is learning, that the body becomes flexible.
It is the same when building strength.......