What he has discovered along the way is a deeper study of happiness that can apply to those with serious mental health challenges, but also to those simply in need of a lift.

But Siva Anandaciva, of the King's Fund health think-tank, says the problems run far deeper than just these 18 delayed projects - and the others that have already been finished, started or approved for this decade.

“The fracturing of community in America is driving a deeper spiritual crisis that threatens our fundamental well-being,” Murthy wrote, calling for a radical shift “in how we build and prioritize community.”

It is nearly finished and will "dig deeper" than the last, she says.

Each edition of Tech Decoded includes expert analysis from top BBC correspondents, who dig deeper into the latest news stories.