An ability to compartmentalize disappointment.
It is ineveitable as entrepreneurs that disappointment will visit us in one form or another...almost on a daily basis. I believe an ability to put disappointments into the right perspective, and then move on, is a much required trait for a successful internet enterepreneur.
I have seen too many entrepreneurs and even public company CEO's let the most incidental disappointments rock their confidence and prevent them from thinking in a productive/creative way.
As a former personal trainer of many CEO's, I had the opportunity to study which ones seemed to steadily move forward, even in the face of an onslaught of disappointments. (specifically quite a few real estate moguls)
Those that were able to compartmentalize a bad meeting, a broken deal, a rogue employee, etc. are still around to fight the fight today.