Whenever I think commonsense I picture Peter Dunne. For 30 years he has been Mr Middle-of-the-Road, a safe pair of hands, the goody-two-shoes of the New Zealand Parliament.
And so, like everyone from the Prime Minister down, I was shocked that he was implicated in leaking a sensitive government report. I struggled to believe it.
No one is more shocked than Dunne himself. He admits to acting "extraordinarily unwisely, even stupidly" but categorically denies leaking the report. He "cannot rationally explain why things happened the way they did".
It's like he was possessed and the Devil made him do it.
It was Dunne's basic goodness that did for him. Politicians leak all the time. Helen Clark was masterful. But they don't get caught. That's because they know what they're doing.
You certainly don't use your Parliamentary email. You don't discuss with a journalist the possibility of leaking. That gives them the power, either through error or design, to get you sacked. If you're going to leak, leak; don't leave your fingerprints all over it.
The leaking, too, has to have a point: it advances your cause, knocks an enemy off course, distracts the media from your own problems, or helps set the agenda. The leak was of no political benefit to Dunne whatsoever.
There is the possibility of an improper relationship with the journalist. But I don't think so.
Plenty of MPs and ministers have had affairs and infatuations, including with press gallery journalists. That's life. But again, they know how to conduct themselves so it doesn't become a problem and, more particularly, so they don't get caught.
Again, it's Dunne's goody-goodiness that has done for him. He could not imagine misbehaving or anyone thinking he would misbehave and so didn't undertake the basic precautions that for others would be elementary.
Parliament is a lonely place and Dunne has been especially lonely, being a long-time party of just one. He supported Helen Clark for two terms as Prime Minister. He's now in his second term supporting John Key. In our tribal Parliament, he lacks a side. His politics are middle-of-the-road and boring. No one is much interested in him.
And then whoosh - a new and engaging journalist asks about his work. He gets carried away. He says a little too much. He isn't immediately struck by lightning. He emails. He's still standing.
And then bang: his 30-year political career is toast. He struggles to explain his behaviour and reads of his misdeeds believing it must be about someone else.
That's the trouble with Sunday School-types. They don't know how to do naughty, and when to run with it and when to leave it alone. They can't distinguish a little bit naughty from too naughty even for bad boys.