There are benefits for the small group of people who are able to push just a little longer than everyone else. But there are also benefits to the few who have the awareness to quit early then refocus their effort towards something new.
Bottom line is, you have to quit the wrong stuff but keep doing the right stuff. The longer you work to try and improve an outdated tactic, execute a broken model, or spend more on the wrong type of advertising then surely you're heading the wrong way.
However, the way you fix the problem is by having the guts to quit early, while you're not too deep in the affray, when you haven't spent too much money, refocus your energy, then apply it towards something new with a higher probability for results.
Quitting is not always a bad thing to do. Sometimes it's the smartest thing to do.