It was like this at first. First of all, you are not used to this movement, not used to chest exertion, and your posture may be irregular. So more is to exercise the muscles on your arms, which requires you to explore gradually. You must adjust your position and movements to find your best posture. You have to experience it yourself, and you don't know what others say, because everyone is different.

Fitness is very skillful and scientific. Stupid blind practice is just a waste of energy.

There is also that when ordinary people start to exercise, the triceps on their arms must be tired first, which is more effective than the chest muscles. This is because ordinary people's triceps are too weak. The pectoral muscle itself is much bigger and stronger than the triceps. If you haven't practiced your chest muscles and triceps at first, it must be the triceps that feel tired and sour first. So when I started doing bench press, the first thing I did was to exercise the triceps on my arm.