When Hollywood film director James Cameron surfaced this week from the deepest place on earth, he was admired for his scientific achievement. We were told about his experience as a diver and the unique data collected on his expedition; about how his latest 3D cameras recorded new scales and distances, and his human eye discovered new details among the waters of the Mariana trench.

If, however, the 11 tonne craft had become trapped, seven miles below the surface, killing Mr Cameron, professional standards would have been applied more strictly. Divers and scientists would have analysed the details of his training and experience. They would have argued that he should have sent a professional oceanographer; or an unmanned craft, which would have been cheaper, safer and (because it could have remained down there for longer and collected more data) more effective. He would have been criticised for recklessness, extravagance and amateurism. And yet these things are exactly what made his journey so magnificent.

It was an adventure: a man separating from his kind, undertaking a terrifying journey, returning as a hero. The scientific data that he acquired may be of minor significance. His adventure is not. Adventurers matter. It was the desire to be a hero that drew Alexander to march his tiny army across the desert and attack the massed forces of the Persian king at Babylon – and, by so doing, to bring Greek civilisation to India. It was a quieter but equal sense of chivalry, patriotism and sacrifice that kept Meriwether Lewis and William Clark moving on to the Pacific north-west, thus making possible the modern United States. And if Mohammed was able to persist, in penury and peril, and keep his faith and that of his followers long enough to lay the foundations of a religion that lives on 1,400 years later in one and a half billion souls, it was because he too had the virtues of a hero.