HIT’s basis is that a short high-intensive workout is enough to stimulate muscle growth. This is the reason for the idea that one set per exercise is enough.

Muscles grow while resting not while training. It’s one of the highest principles: there must be more relaxing- than training days.

Nobody pays attention to the “pump effect”. It must be seen as a simple heaping up of lactate (milk acid) inside the muscle, not as an indicator for muscle increase.
Maybe this could be a mistake? Is it possible so much volume disciples are wrong? Please read on.
HIT is very rationalized. It’s not about the feeling during the training, it’s about the result. A training unit should primarily be productive. Besides that it should be fun.
You try to give your best in every set to get the maximum out of your training.
Because you can reach your maximum just once, it’s reduced to one set per exercise. Some coaches recommend more than one set for each exercise, but it’s the same problem like in volume training. Nobody can really explain why.