Most of the time they stay around too long, their brains so encrusted with the scar tissue of blunt political trauma that – like broken-down boxers or creaking footy players – they demand to play on, incorrectly believing they've still got it in them.

This happens both in leaders who have genuinely aged (Howard) and those who have aged prematurely (Gillard, Rudd).

But every now and again, someone resigns. Resignations are a science all their own.

There are thousands of variables intricately woven into the formula that determine whether a resignation will be a good one or a bad one.

Don't get me wrong. A “good” resignation is still a career-ender. “Operation a complete success, patient still dead” is the best you can hope for in these circumstances, but legacy is important in politics. If you are young – like Barry O'Farrell – it's much nicer, when later going about your business as a private citizen, to be slapped on the back by people who thought you went too soon than slapped in the face by people who still can't forgive you for sticking around.

The first point in the discipline of successful resignation is deciding whether it's absolutely necessary. The sweet spot you're looking for here is the point at which it's very nearly necessary, but not quite.

That way, the element of heroic sacrifice is preserved: He resigned, as a matter of honour.

Here again, the elements are famously slippery.

Was, for instance, Barry O'Farrell's resignation necessary? Technically – no, not at all. Of all the public figures who have trooped through Sydney's Independent Commission Against Corruption in recent months, Mr O'Farrell is firmly and obviously one of the good guys.

But in this field, the tiniest detail can throw you. A bottle of Grange from your birth year is a horribly memorable gift, and thus twice-cursed; not only is it hard for anyone to believe you can't remember getting it, but it also makes it harder for anyone to forget that the whole thing happened.

It's as sticky as a Wiggles chorus, and Mr O'Farrell would be in much less trouble had the thoughtful Mr Di Girolamo just sent him a horrible print worth $3000 instead, or a framed Wallabies jersey, or any one of the other overpriced trinkets that people like Mr Di Girolamo regularly flog off at party fundraisers.

Plus, booze is troublesome; it just is.

Whether you drank too much of it and drove into a gate, like former West Australian treasurer Troy Buswell, or stuck your willy in a glass of it, like the Queensland MP Peter Dowling, or nicked two bottles of the stuff like former Democrats leader Andrew Bartlett, liquor is a leading cause of politicians deciding to spend more time with their families.

Punctuation is important.

In the thank-you note – written, damningly, in the Premier's own corpulent hand – Mr O'Farrell thanks Mr Di Girolamo for “all” his help.

To a later reader, that single pen-stroke conjures a multitude of further gifts, the dancing girls and Faberge eggs of the imagination sketched out in the sickeningly rich colours of the ICAC palette. Personally, I think the whole thing was survivable but for the underscore, but I am especially interested in punctuation and thus possibly an unreliable adjudicator.

The most important factor by far, though, in a successful resignation, is timing. You have to do it early; ideally, before anyone has called for it. A voluntary resignation is surprising, affecting and heroic. A resignation offered by a quarry who has been bailed up in their own home for three days by a crowd of angry people carrying torches made of petrol-soaked rags is less of a good look.

By these and most other standards, Mr O'Farrell has had a good resignation.

But that's the tragedy of the week, too.

The very fact that a spectacle like this is so rare and shocking – a public figure deciding not to give himself the benefit of the doubt – is in itself depressing. And the resultant cry for more regulation, a “crackdown” on lobbying and so on, ignores the basic, awful lesson of ICAC, Craig Thomson and all the collected murk of recent years.

Some people won't take an ounce of responsibility even when caught absolutely bang to rights.

Others will resign even when they could probably have got away with sticking around.

It's impossible to legislate for that kind of thing.

In fact, the answer more probably lies in less regulation. Less of the centralised party controls that kept Eddie Obeid and Craig Thomson in Parliament for so long, and nurtured operators like Nick Di Girolamo.

More involvement from ordinary people who know a shonk when they see one. Especially if he's a shonk bearing plonk.