If you think only tech issues, budget, (nasty) bosses, etc can derail a beautiful projects, think of when mozzies attack.
A big determinant is the Mozzy.
Mozzies are simply mosquitoes, especially the ravenous types, who think we human beings are the most delicious things walking on two legs. Get any of these dudes to bite a key guy on any project; the direction of the project days after is better left to imagination.
I recently got mugged by a group of very devilish Mozzies, had to spend two days at home recovering from their bites (and the resultant malaria..) while my outstanding deliverables were left undelivered in the office. What a shame!