Question about HU plays

I recently started studying heads up plays. That includes watching high stake heads up plays as well as studying some math.
One thing I have realized is that these so-called HU specialists who are winning players go for gutshot straight, runner runner flush etc. Normally, runner runner or a pair draw with like a T high etc are normally considered as mathematically bad plays.
I understand that it depends on how other players play and situations. However, I see these runner runners alot by HU winning players.

What I am wondering is how can you really tell if the guy is really goood when watching HU plays.
What kind of qualities make him such a good player?

Advice of any articles or links for studying HU games? [img]/images/graemlins/cool.gif[/img]