Easier not Harder
The goal of training should be to make things easier, not harder. The popular approach for most is to constantly make things feel harder, leave you gasping for air, or lying in a pool of sweat (or worse vomit).
There is nothing wrong with working hard, or challenging yourself. It just needs to be done in a systematic way. And every training sessions should not leave you feeling crippled.
In virtually every other discipline in life we learn the fundamentals first, and then build into more complex aspects of that field. In reading/writing we learn letters, then words, then how to construct a sentence, punctuation, and so on. In match we learn addition, then subtraction, then multiplication, then division, and so on. In music we learn notes, scales, then songs.
Yet when it comes to movement we tend to skip the basics. We jump right into complex boot-camp workouts doing complex movements like sprinting, jumping, weightlifting/Olympic lifting movements. We don't do a few good reps at slow controlled speeds. We load them up to max levels, do them until exhaustion and at high speeds. We skip over and fail to master the simple things like breathing, posture, and foot positioning/engagement. We can't crawl, skip, or do a decent push up, yet we jump right into advanced core exercises, bench pressing, and running at high speeds or long distances.
Many of us would be better served mastering our fundamental movements, and trying to make things easier/more efficient. This in turn will allow you to more robustly take on a variety of tasks, with more ease and more resilience. Much like nutrition, we don't often need harder, or longer. We simply need to practice the fundamentals consistently for a long time and approach our physical education much like we do other disciplines in life.