In yoga class we are often put into poses that may not feel the most comfortable. All your muscles may be shaking, heart pounding, hips screaming... and your about to give up and lay flat on your mat the rest of class. And then for some reason the teacher, as if they know exactly what you are thinking, challenges you to STAY. Stay with your breath, your body, the moment. Who cares if its uncomfortable... your not dying (hopefully although it may feel like it). Truthfully you are only getting stronger in those seconds. Your very body is witnessing that even when you think you cant do it any more, you can. The limits you have set in that pose have been crushed, and you have redefined yourself.
Remember when you were younger and a lot of life came as a surprise to you? You weren't included in the plans, you just loaded up in the car when ever the family told you to, half the time not even knowing your destination. Every day was welcomed with a sense of mystery, wonder, experimentation. Wasn't that fun?