is head of the BBC College of Journalism
There's nothing the media like more than seeing a politician wrong-footed by a voter. Think Tony Blair and Sharon Storer. Think Gordon Brown and Gillian Duffy.
So when David Cameron was challenged by a senior Harrier pilot as he prepared to announce big defence cuts on Tuesday, it was no surprise that the exchange featured prominently on television, radio and in all the following day's newspapers.
Lieutenant-Commander Kris Ward asked the Prime Minister:
"I am a Harrier pilot and I have flown 140-odd missions in Afghanistan. I am now potentially facing unemployment. How am I supposed to feel about that please, sir?"
Mr Cameron is not a defence expert, and his response demonstrated a less-than-secure command of the brief.
"The military advice is pretty clear. When we have to make difficult decisions, it is right to keep the Typhoon as our principal ground-attack aircraft working in Afghanistan at the moment and it's right to retire the Harrier."
Doubtless he'd been well briefed and well prepared for questions just like this, in readiness for his statement in the Commons a couple of hours later. Unfortunately for him, he got it wrong.
The Typhoon is not our principal ground-attack aircraft in Afghanistan at the moment. The Typhoon wasn't even designed for ground attack and is only now being fitted out for that role. And the RAF has never deployed it in Afghanistan.
It might have been excused as a slip of the tongue on any other day. But when you're about to announce the details of a wide-ranging defence review, it was surely a bit more serious than that. It was a potential gift to anyone who didn't like what he had to say - and there were plenty of those.
Yet the Prime Minister got away with it. There were no hoots or snorts of derision from his hosts - members of the military, many of whom must have spotted the lapse but were presumably too polite to mention it. Nothing either from any of his critics in the Commons - sitting behind him as well as opposite - who could easily have used it as a stick to beat him.
And although almost every newspaper featured the exchange in some detail, only one - the Times - noticed the slip. It reported:
"Mr Cameron ... added insult to injury by referring to the Eurofighter Typhoon fighter jet rather than the Tornado GR4 as the ground attack aircraft that would be retained."
Mr Cameron still came in for plenty of ridicule when he announced the building of aircraft carriers that would not be carrying aircraft. But the clanger that might easily have caused him greater discomfiture had it been turned on him was allowed to pass unnoticed.
But if you're going to slash the armed forces one day and half a million public sector jobs the next, you probably need all the luck you can get.