Late in this book of biographical essays, David Runciman discusses how Barack Obama took consolation from the thought that each of us is but a blip in human history. Runciman finds this “a little disappointing”. I would go further — it is a devastating thought that even a man bestowed with such gifts as the former US president might search world history for comfort in his own triviality. What was it all for?

It is also a well-chosen insight in a book full of them, and captures nicely its overall theme: what gnaws at those at the top are not the bad decisions but a stifling sense of impotence. As US President Harry Truman said of his successor, Dwight Eisenhower: “He’ll sit here, and he’ll say, ‘Do this! Do that!’ And nothing will happen.” In Runciman’s words: “the power they had imagined was illusory”.

As a recently departed adviser in Downing Street, these words cut deep. When I took the job, a former colleague teased me about the lack of levers I would have to pull. I spent two years learning what he meant: outside of war, no politician can just order their policies into existence. There are layers of people, laws, money and custom to wade through before anything starts to change. When you take power, you think the point is to have smart ideas; when you leave, all your praise is for the rare officials who just know how to get things done.