The funny thing, however, is how often this rule is forgotten as soon as we switch from the fitness world to the healthcare one. Oftentimes, I'm witness to individuals in pain who have received prescriptive exercises from a therapist, but have attempting to use that same movement - and same volume - for months or even years!
This is essentially the same as trying to gain bicep size by curling with the same-weighted dumbbell for the same number of sets for a year. How effective do you think this would be for initiating physiological change?
Perhaps we get stuck in the mindset that injured or pain-afflicted clients should not be taken to realms of discomfort. Fairly enough, even many clients are hesitant to exercise beyond a very mild comfort level. Let's remember, though, that there's a difference between the healthy discomfort of a challenging exercise and the noxious sensation of when it becomes to be too much. (This is part of the reason why I allow my clients to work through a 3/10 pain scale, the other reason being so as to not train their nervous systems to avoid pain.)
Long story short, challenge the tissue and be mindful of the pain, but don't totally avoid discomfort. (Am I starting to sound contradictory? Welcome to healthcare.) All in all, we need to ensure that we're varying the intensity and type of movement. After all, that's life!