How do manipulative people end up making someone so miserable?

I've seen some people have a tendency to really ruin others mind n make them feel miserable n obsessed w them. How do they do it? Is that something that comes naturally or something people do knowingly in order to manipulate the other person? How do we even identify these sorts of people? They seem really perfect on the outside, unaffected by external taunts n unwanted insults...like really really confident, but then, they suck all the energy out and drain u dry... Unless you've come out of that zone, I dun think it's easy to notice manipulation...or is it??