There is a common thread I notice in many of the yoga classes I teach, and, I assert it's a commonality of yoga practiced in Western cultures. I see so many students pushing themselves in yoga class - to the point of susceptibility to injury.
I often talk about finding your edge - the perfect place, that only you can know, between effort and ease. Effort includes focusing on the breath, minding your alignment, and accepting modifications when needed. Toughing it out is not that.
Toughing it out means abandoning the breath, and forcing the body to go where it shouldn't in order to fulfill the unreasonable expectation we've set for ourselves for the practice. It's as if our worthiness is determined by the level of difficulty we achieve, and the corresponding amount of sweat generated in the process. We attack our practice with a "no pain no gain" attitude.
We seem to think there's somewhere to get to, versus locating our self on the path of a mindful and forgiving journey. The Yoga Sutras actually prescribe yoga postures to be "steady and comfortable".
In her book "Living Your Yoga", Judith Lasater laments that we do not practice to find the comfortable, but to overcome ourselves and conquer the pose - clearly not meeting our body where we're at in the moment.
In your next class, notice where your mind takes you. Steady and comfortable? Stay present with the breath, and allow movement to follow in a way that honors the vessel that houses your spirit.