I always like telling the story that aeroplanes legally have to have ashtrays in the toilets. The natural response from most people is “but smoking is illegal on a plane” and well, yeah, it is. But since when did something being illegal mean people stop doing it? If someone needs to smoke, they’re going to smoke. By installing ashtrays you can at least contain the risk.

That’s what almost all software interaction design comes down to; nudging people in the right direction most of the time and (hopefully) preventing them from shooting their own foot off when they get it wrong. On the opposite end of the spectrum, there’s the dark patterns. These are fascinating studies into how to abuse the human mind for the benefit of the system and not the individual.

We’ve all seen them. Opt-outs hidden in lists of countries. Wording so opaque you have no idea if you’re signing up for a credit card or selling your first born son. As an industry, we’re getting better at stopping them. More and more regulations are being introduced for the worst offenders as well.

I learnt of a brilliant dark pattern recently, one I hadn’t heard of or even thought of. It’s used by sites with a subscription service as a way of preventing users from leaving and has two parts.

Part 1: sites have to notify you when your subscription is up for automatic renewal. So in the weeks leading up to this date, they begin a deluge of email. Your inbox grows and grows and they count on human apathy to just click “delete” after the first few dozen.

Part 2 is the genius bit, using systems against themselves. The company starts sending to huge lists of bought email addresses. Anyone who’s ever been involved in campaigns already knows this is a huge red flag, guaranteed to send your rep into the red zone and result in every email passing-go and hitting your spam folder.

Legally, the company are completely in the clear. They’ve sent out a reminder email. It’s your fault if you didn’t check every-single-other-email they sent you.

At the end of the day, patterns are useful. You just gotta pick the right one.