Very agree, and I'm doing this way to train my kids. But the problems is the 老人家 so spoil them. And I always argue with the 老人家, they always think that they are still small, will understand later. But this generation is totally different than before. Nowaday, the kids so smart and learn so fast. I try to 講道理 to them since under 2yrs old. They will understand and know what they do. But sometimes cannot control their temper jei.
My son is 6yo. A lot of kids will start "hitting" people after 2yo as an exploratory act, trying to experiment and find out what they themselves are capable of. If this act is not explained to them properly or stopped within a reasonable time, it will become a "habit".
My suggestion is
1) explain it's not nice and why
2) hold the kid's hand and hit him with his own hand, first lightly and then hard. So, he understands what it feels like to be hit.
This is different from hitting him yourself, cos in theory he hits himself, same way/ hand he hits you. So if he does not like being hit by himself, others don't like being hit by him either.
I find the above more effective than send him to the quiet corner as a 2 yo cannot immediately understand/ correlate hitting and being sent to the quiet corner. Seems 2 different incidents. If you ask him later, he will only remember you have sent him to the quiet corner without remembering the reason why he has been sent there in the first place.
However, if you hit him using his own hand, he will remember he hit himself!! And he will wonder why!! And then he will remember.