As you said, there's pain and then there's pain. And people who aren't that good at recognizing what kind of pain is normal when training and what isn't.

I get these kind of questions and notation almost all the time:
"My muscles were sore the next day and the day after that, what did I do wrong?"
"I felt a sharp pain in my shoulder but kept going on because no pain, no gain, right?"

So two kind of people that probably need entirely different answer. Shortly said the answer to the first one could be something like this: "This is what it should feel like." And for the second one: "Stop training, go see a doctor." Of course I would say also something like: "If you have any hesitations, see a doctor or a physical therapist."

Thing is, some people hear only what they want to hear. If they want to train with the pain, they train and brake themselves. If they don't want to train and feel that the muscle soreness is bad, they find every excuse to reduce their training. And then there are those who just do not know their bodies and when they should do more or those who should train less.

It's a constant struggle. To make some people move more and force some people to rest. I'm sure you know how it is!

Interesting matter is that I have found a few patients who came to me for injectable pain killers due to the pain acquired during strenuous exercise.

Oh. Uh. Darn. I think I've met people like this.