As revelation piles upon revelation in the David Petraeus scandal, the limits of where one thinks it could end up expand too. By the time you read this, we will presumably have been told that Jill Kelley, the woman at the heart of the affair, was being bombarded with lovelorn messages by someone senior in al-Qa'ida, or that Jimmy Savile was actually in the CIA. As the crisis builds, I assume those who chose the less-than-discreet Petraeus to lead the intelligence organisation can only think: we probably should have gone with a spy.

Whatever the geopolitical consequences of Petraeus's indiscretions – and they will be serious – it's the sheer daftness of the human frailty on display that makes the casual observer scratch his head. I think this about footballers sometimes. If you're a striker who wants to sleep around with people likely to kiss and tell, sure, knock yourself out. Just don't also get married.

If you're the head of a spy agency? Well, probably sleeping around is never going to be a great idea. But if you must indulge yourself, for God's sake, don't send any emails about it! Don't do it with the woman who is writing a book about you who has gone on record to say you are a marvellous guy! You are the head of a spy agency! Someone is going to figure it out! Also, as a sidenote: if you are an FBI staffer bringing the case to your agency's attention, do not send anyone involved topless pictures of yourself!

It's striking how often this is the primary reaction to a scandal, whether it's Petraeus fooling around or Margaret Moran claiming £2,000 expenses for a phone that didn't exist: how did they think they'd get away with it? Then again, perhaps my incomprehension is naïve. Maybe this kind of stuff is just part of the human condition. A lifelong-member of the clandestine services could be prone to the same idiot urges as Petraeus was, and even if they might have covered their tracks a little better, they could still have been found out in the end. If this is the case, the only real lesson, beyond the operational ones that the US government must concern itself with, is this: people are wallies. They can't help themselves. No level of success or importance can diminish this.

But I fear there's another possibility: that such behaviour doesn't carry on in spite of being detected, but because, in fact, it almost never is. Men like Petraeus, and those gadabout footballers and expense-claiming MPs, did what they wanted precisely because all the evidence suggested that they would be able to carry on regardless. In the aftermath of a scandal like this, it's tempting to think we've exposed the scandal, and now everything should go back to normal. It seems rather more likely that we've actually barely scratched the surface.