There is PAIN. But there is also Pain.

Another fast point to make.

You know when you stub your toe on the metal bed frame or coffee table leg.  That is PAIN.  All CAPS: PAIN!!!   Yyyooow!

If you have a pinched nerve in your spine, that can produce strong, life arresting PAIN!!!   

As you work with your Posture Alignment Therapist the PAIN is starting to become a bit intermittent then even more intermittent (a good sign your body is becoming more balanced, dormant muscles are starting to work again, joint and bone positions are improving slowly).  Your therapist may be explaining your right buttock muscle is atrophied and has been out to lunch doing nothing to move your leg at the hip.  This is often due to the poor rounded upper back position which DEFINiTELY limits by 50% or more full hip function.   

Getting atrophied muscles to contract and function again can in and of itself produce discomfort which some people lump in with really horrible PAIN.  
"Pain" without capital letters may no doubt be a strong sensation but it's not the same PAIN.  It's a different pain.  Atrophied muscles can take some time to improve.

If it's Pain and the person associates it with PAIN, then they can easily become afraid that they are doing something BAD and should stop.  The therapist isn't a mind reader but in many cases being very experienced with many types of clients and problems know that stopping from fear of Pain (not PAIN) is counterproductive and will limit sometimes dramatically the therapy process and progress.  

The therapist will encourage continuing since the tug of war between a dysfunctional muscle or joint and the healthy function the exercise is asking for will result in more healthy function, less PAIN and less Pain.