Somewhat related, but my view of suffering really changed after reading "Man's Search for Meaning".
I still have that pain almost a year later, multiple MRIs and orthopedics have been unsuccessful in finding out what it is. I'm only now able to run very short (2.5km) distances. Pushing yourself to ignore pain is very possible and can be very dangerous.
Pain should be a signal to consider carefully what you are doing.
I consider myself reasonably fit, but I’m not sure any of the activities I do strictly require physical pain. Soreness? Fatigue? Sure. But rarely pain, unless I’ve made a mistake.
A big part of this is that people inexperienced with pushing themselves will mistake the soreness and fatigue for pain and quit. It's easy for you to say this because you claim to be "fairly fit". You have experience beyond average (at least in the US).
Also, if you are overweight, did not exercised for long, but are ambitious, that is the prime situation where it is easy to cause yourself an injury. Fairly fit means that your body is adjusted exercise at least somewhat and joints and such can withstand.
When I realized how stupid the mindset is and how deep in me that mindset was, it was too late.