Does this advice work for any difference in sizes between the people? I suspect if one is so small as to not pose any threat at all and/or take on extra damage, it would end badly for them more often than not.

For me... yes. I was significantly smaller and was only able to weakly punch his chest. I got punched in the face and got a black eye and a sore skull.

As an adult the concept works. Bees can’t hurt me significantly, and even when they land an attack they die - but I go out of my way to leave them alone.

> I suspect if one is so small as to not pose any threat at all and/or take on extra damage

The trick is to turn off the switch in your head that tells you to stop if you're in too much pain or something is very wrong. Only real lunatics will keep going at someone that fights like that, and those are pretty rare.