Back in May, before Donald Trump was even officially the Republican party's candidate for president, Business Insider's Josh Barro tweeted something that's stayed with me:

"I can't do that; it would be embarrassing" is an important impulse for humans to have. Trump doesn't have it. — Josh Barro (@jbarro) May 31, 2016

I've thought about that tweet a lot since. Partly because so much has happened to confirm Barro's diagnosis; partly because, as someone who is capable of feeling acute embarrassment while alone in an empty room, I find the complete absence of it weirdly compelling.

But over the weekend, as the whole Mike Pence-booed-at-Hamilton mess was blowing up, Trump's obvious lack of embarrassment suddenly felt sharply, painfully relevant. The problem is not that he will, say, demand an official presidential portrait in which he's stripped to the waist and wrestling a tiger. The problem is that being unembarrassable will make it a lot harder to hold the president elect to account.

One of the things that keeps us on the straight and narrow in life is the fear of looking stupid in front of our peers. It would be quite easy to skip the odd bus fare, or pocket the occasional chocolate bar from the corner shop without paying for it. Getting caught would incur legal or financial consequences but they're not huge, in the scheme of things, and the chances of getting caught are slim.

So why do most functioning adults not commit these petty crimes? Partly because of morality, yes, but partly, I suspect, because it would be really, really embarrassing if anyone found out. (“You're a 45 year old commercial banker and you're shop-lifting like a kid? LOL, what's wrong with you, you sad case.”) The fear of looking silly helps stop us from doing a huge range of things we might otherwise profit from doing.

The problem with Trump – a problem with Trump – is that he has no such fear. There's no rule requiring US presidents to place all their assets in a blind trust, so that they can't be accused of profiting from the presidency, any more than there was a rule requiring them to release their tax returns. It's just what they've always done, as an easy way of demonstrating their propriety. To do otherwise might look bad.

Trump, though, doesn't care about looking bad; doesn’t even seem aware it’s an option. So not only is he ignoring the blind trust convention, he's already set to profit, albeit unwittingly, from his new role. (Sample headline, from Gothamist: "Foreign Diplomats Lining Up To Stay At Trump Hotels But Definitely Not To Curry Favor With Trump".)

This doesn't just look bad – it is bad. But without the mechanism of public shame to impel good behaviour, it turns out, the sum total of what anyone can do about it is nothing. Public shaming is one of the most powerful mechanisms through which the media and the opposition can hold a politician to account. The Trump presidency has instantly rendered that mechanism entirely toothless.

Some business improprieties are the least of it, though. Why have former presidential candidates not said they’d refuse to accept an election result if they lost? Why have they been so reticent about publicly attacking their critics? Why have they not appointed alleged racists to senior posts? Pursued policies which will demonstrably roll back decades of progress on civil rights, marriage rights, abortion rights? There are many reasons, of course, but a big one in each case is – because they would look bad. Because people would criticise them for it. Because it would be embarrassing.

As Barro noted back in May, the fear of being embarrassing is a key impulse that stops human beings from doing bad things. Trump doesn't have it. Who knows how many other conventions of behaviour the new president will throw out, because it turns out the only thing keeping them in place was shame.