That is a saying that is very true. When I see someone who is big and in great shape I know that there was pain endured to get there. Not just the pain of a strain muscle but ligament pain and joint pain and pulled muscle's. That is what makes me apprecaite that person.
Sometimes you have to fight through the pain and keep pushing it. I spent a year solid that every time I lifted on shoulder or bench every rep especialy at higher weights hurt on my left shoulder first then my right. Knowing if I just kept pushing I would get past it and I have.
This brings me to my point. I hear it in the gym and on some threads of people talking pain. Some are legit issues and need to looked at. But you got to ask yourself are you hurt or being a wuss. Is some pain and discomfort gonna stop you from your goal? I believe the person who came up with NO PAIN NO GAIN understands what I am talking about.
Peace