THE VALUE OF OPTIONS, even unexercised ones:

“Closing a door on an option is experienced as a loss, and people are willing to pay a price to avoid the emotion of loss,” Dr. Ariely says. In the experiment, the price was easy to measure in lost cash. In life, the costs are less obvious — wasted time, missed opportunities. If you are afraid to drop any project at the office, you pay for it at home.

Heck, I wrote about this in the Yale Law Report years ago. (Warning, big PDF file).