CT has answered this previously but I feel compelled to jump in because my initiation into weight training was through the HIT school. Failure, according to Ellington Darden, was the inability to do another rep in strict form. Classic example is a BB curl, where there should be no body English, full ROM, and always a controlled eccentric. Further, you were meant to do this with a relaxed face! This should put the effort required into perspective. I also think if you can adopt this you’re less likely to burn out, as well as suffer injury of course.
Don’t get me wrong, I grind out some shaky reps on BDW but generally try to adhere to that advice. I still recall some old HIT sessions where I could nap on the floor minutes after a workout, thanks to some serious neural fatigue. Clearly, this is counter productive and highlights one of the weaknesses of using this as an exclusive system, in my opinion.