The question is somehow difficult to ask. What is he talking about? About the blow? About the combination "two"? About hitting a lightweight? About the knockout blow? About a strong blow?
So, how does a "shit" in theory drop a bad grade? His strikes are as sharp as possible, he puts enough mass into them.
In theory, because you still need to hit the target, and it needs to be done on time.
Regarding the "two" ", you need to understand which of the blows to disassemble. Maybe the first one is just distracting, and the second one turns out to be accented. Or maybe on the contrary, the first is enough, and the second may be "past", but the person has already "left" the first. I often had the second option, the left hand is weaker, but the blow is faster, they did not have time to react to it. But the right one has already gone into "milk".
Total: the mass does not matter if this mass does not take part in the impact. The force of the blow does not matter if you missed. It is also important whether the enemy sees the blow or not. Did they just hit him on the head or not. In what position it is (stable or not)
There are a lot of nuances. For everyone who wants to figure it out, the way to the gym to the coach (boxing, hand-to-hand fighting, Muay Thai). If the coach is normal, he will be able to explain. If good, he will even be able to teach how to use his advantage (skinny or, on the contrary, a large mass).