Of the 10 principles of war taught to all cadets at Britain's Sandhurst military training academy, coping with “surprise” is among the most important. General Stanley McChrystal has had to tackle many potentially career threatening surprises during his tenure as commander of US and Nato forces in Afghanistan, from suicide bombers to unreliable Afghan political partners. But it would be fair to assume that he can never have expected to be undone by an article in Rolling Stone, one of America's premier cultural magazines.

Gen McChrystal took over in Afghanistan in 2009, in inauspicious circumstances. His predecessor General David McKiernan had been the first US general to be relieved of command during a war since General Douglas McArthur was pulled out of Korea. But he came with an impressive record, an adventurous reputation and made good first impressions.

His revised strategy for Afghanistan soon became the McChrystal plan or, even more grandiosely, the “McChrystal doctrine”. It showed a feel for counter-insurgency that energised troops on the ground. One of my friends – at the time commanding more than 200 ISAF troops in central Helmand – described it as the most encouraging document he had ever read by a general.