As the tough commander of the US war effort in Afghanistan is removed from his post, the BBC's Lyse Doucet remembers a previous meeting with the popular general, Stanley McChrystal, when considering how he slipped up.

General McChrystal looked down at his boots.

He was strangely quiet, distant, as we sat facing each other on straight-backed chairs, waiting to start our interview.

I wondered what weighed so heavily on his mind.

He was usually so quick to smile and talk.

I knew he had just come from the presidential palace. Questions raced through my mind.

Had something gone wrong again with President Karzai? Or on the battlefield?

To break the silence, I simply said: "Tough job."

"Yes," he replied, "I just heard my college room-mate died. He's been ill."

"Oh, I'm sorry," I said. "Would you like more time?"

"No," the general insisted, visibly tightening his jaw and sitting up straight. "This is my job." And the general focused.

That was Gen McChrystal in the field, in his element, in command.