Megaprojects can be identified by their size -- in the Billions -- and also by the fact that most of them are considered a failure in terms of cost overrun, delay or the benefit delivered. Why do over 90% of such projects fail? Professor Bent Flyvbjerg of the Said Business School at Oxford University has spent his career finding out. Together with his teams he has collected lots of data about successful and unsuccessful megaprojects, and has also developed tools to help such projects increase the likelihood of success. In this episode, Bent gives us an insight into his important research.