yeah, with my recent return to cycling after about 8 years off, I went from 50-miles a week to doing double-centuries within a month. Knowing that quality of training is better than quantity of training allowed me to regain 90% of my previous fitness in just 1/10th the time.

However, there's a difference between pain and suffering. Personally, I always stop when I feel pain because it's a danger sign.

Suffering, on the other hand, is just discomfort. Like doing sprints and intervals; the lactic acid, the tight z-bands in the muscles, the maxed-out heart-rate; that kind of suffering I actually enjoy! Benefits comes in heaps and bounds when do you that extra 3-5 secons at the end of a sprint when you think you've given 100%. Extending the 1-minute interval at 95% effort an extra 10-15 seconds will allow you to do that minute even faster the next time. Suffering ends soon enough.

Pain that lasts longer than a couple hours? Like sharpness in the joints, pointed and heated spikes in the muscles, etc. should be attended to immediately.