Dozens of people in one meeting. One promotion. A week later, someone walked into the manager's office with a project he had never promised.

Years ago, before I ran my own companies, I worked for a multinational. In my department there were dozens of us in the same role, and that year there was one promotion on the table. Everybody knew it. Everybody wanted it.

Most of our meetings were online. Thirty, sometimes forty faces in little squares, half of them with the camera off. You know the kind. One person talks, the rest answer emails, and at the end nobody can tell you exactly what was decided.

In one of those meetings, the manager went round the squares and asked each of us to take on a project. Out loud, one by one: who does what, by when. Everybody said yes to something. I said yes to mine. One of the quieter people in the team took on a project that everyone could see would get noticed.

A week later, one of my colleagues walked into the manager's office with that project, finished. It was good. Well thought out, well presented. It just wasn't his. He hadn't said a word about it in the meeting. Someone else had promised it, and he had delivered it as his own, in the one week of the year when it mattered most.

He wasn't stupid. He was counting on one thing: that nobody remembers a meeting.

Forty people, an hour of talk, cameras off. After a week, a meeting stops being what was said and becomes what each person remembers was said. And what people remember is usually what suits them. He said, she said. Your word against mine. In most companies, that argument is won by whoever is louder, or closer to the manager.

Except this meeting had been recorded.

The manager didn't argue. He didn't ask anyone what they remembered. He opened the recording, went to the minute where the projects were handed out, and pressed play. Everybody heard who had said yes to what.

The conversation was over in less than a minute.

A meeting nobody can replay belongs to whoever remembers it most conveniently.

Most people who get a meeting wrong aren't lying. They genuinely remember it differently. A few are doing what my colleague did, and hoping the fog of forty voices will cover them. From the outside, you can't tell the two apart. A recording doesn't need to. It settles both, without anyone having to accuse anyone.

Think about your last month of meetings. Who said they'd send the figures? Who agreed to the deadline? Who promised the client the extra visit? If the honest answer is "I think it was...", you don't have a decision. You have a rumour, waiting for someone to use it.

So wherever I've run things since, the rule has been simple: if it was decided in a meeting, it has to exist somewhere other than people's memory. Otherwise it didn't happen, and sooner or later someone will say it happened differently.

If it was promised in a meeting and nobody can play it back, it isn't a promise. It's an opinion about the past.