Seriously, I can't believe that's the top comment.

Accepting the counter offer can sometimes make sense though. A friend of mine got a call from his previous employer offering him enough of a jump that it would be hard to turn down, but likes his new job better so he took the offer to them and they matched it. That was most of a year ago and they've been very good to him so far.

The degree to which different Employers/Roles actually care about retention varies, but those who do will go out of their way to placate people they think might be flight risks. The cost of awarding a small "market adjust" is smaller than letting the position go vacant.