However, Dan Ariely has explained that the secondary effect is potentially more powerful. For those that choose to stay, they will forever live with their past action of having turned down lots of money to work there. So, when they're having a crappy day and hating their job, they're probably thinking "why didn't I take the money and quit?!". The only way to reconcile their thoughts and actions is to explain that, in fact, they must really love this job and therefore should work hard at it. This effect is known as ‘Cognitive Dissonance’[1] and is fascinating.
Here's a link to a video of Dan explaining this[2] and a really excellent Coursera course he does on Irrational behaviour[3].
[1] http://en.wikipedia.org/wiki/Cognitive_dissonance
[2] http://bigthink.com/videos/dan-ariely-zappos-and-the-offer