Often we stand in the way of our own practice, without even realising it. This is something I see with students who have injuries. They tell me, “I can’t do this posture, or that posture,” before they even try!
Obviously if you have an injury it is important to follow medical advice and take it easy, but don’t slip into the mindset of “can’t.” You should always try to do at least a little bit of a posture, even if it is just the set-up. If you don’t take the first step you won’t make any progress towards healing.
The same is true if you are just having a tough day. The point of Bikram yoga is not doing every pose perfectly, but always trying and using those small efforts to help you improve every day. By focusing on the moment you train both your body and mind to move past the barriers you face.