Branson has never been someone to back down from an idea because others criticized him for it and admires those who take the risk on something extraordinary.
That said, Branson never jumps into a project that will ruin him if it fails. It's a lesson he learned from his father, who allowed him to drop out of school to start a magazine as long as he sold enough advertising to cover the cost of printing.
He uses the investing term "protecting the downside" to describe this limiting of risk, and it's how he convinced his business partners to join him in making the huge leap into the airline industry in 1984. They could trust him to pursue this seemingly ridiculous idea since he got Boeing to agree to take back Virgin's one 747 jet after a year if the business wasn't operating as planned.