Extravagance. I see less of this these days though I have seen penny wise, pound foolish activity.
Taciturnity. Rapid progress and constant adjustment in a new endeavor requires continuous communication of these changes.
Greed. Holding too tightly to the percentage of ownership figure doesn’t allow room for a company to attract the leadership, employees, and investors that will maximize shareholder value – including the founders’. In a chat my partners had with Mark Leslie (Veritas founder/CEO) he mentioned that when there's a success it's rare someone complains they had 2% rather than 10% and conversely by not bringing in the right resources (while holding onto equity) companies often are doomed to fail and 10% ownership of nothing is exactly that.
Arrogance. There is a fine line between a beneficial pride of confidence and a dangerous arrogant hubris.
Indecisiveness. The beauty of a startup is that there are endless possibilities. The difficulty is to concentrate on one opportunity, not every opportunity. David saved his best for last -- I couldn't agree more.