My favourite definition of leadership was shared with me by Michael T. Williams back in the 1990s. He was a South African barefoot water-skiier and motivational speaker and coach.

Leadership, he said was “the ability to articulate a vision, and through yourself and others, cause that vision to become a reality.”

As a 20-something in my first PR company, I was very impressed with the “through yourself and others” part of the definition. I had employed two staff and was battling to get them to pay attention to their spelling, let alone all the other things that go into servicing PR clients. Spelling is important in PR.

But it was in 2011 when I ran my first big organisation — 2,500 members, nine countries, 38 senior managers, a board of six people — when I realised where the true power of that definition is.

It’s in the first bit: “The ability to articulate a vision.”

When you’re running a big organisation, that’s basically all you’ve got. Your ability to get things done is directly tied to your ability to get people to buy into your vision. It’s not called “sell-in.” It’s called “buy-in.” Your vision has to be compelling and attractive. Else nobody will buy it.

If you look at the stories we tell about leadership you’ll find it’s usually about something somebody said. It’s about language. About a speech.

The sporting movies are full of coaches at half-time exhorting their team to higher performance. The war movies are exactly the same, starting with King Henry V just before the Battle of Agincourt in Shakespeare’s play. (If you want to see the speech, just search for “St Crispin’s Day Speech.”)

It’s so well known that a phrase from that speech “band of brothers” ended up as the title of an Emmy and Golden Globe winning miniseries by HBO (produced by Tom Hanks and Steven Spielberg.)

When we want leadership from our politicians, what is it we’re asking for? We’re asking them to make a speech. We’re asking them to “articulate a vision” for the country, or the province, or the city. That’s what we read about in the newspapers. What the politicians said. Not what they did. For a politician, doing something is often just saying something.

I knew that rhetoric was important. I was fond of entering speaking contests and had achieved some success. But when I was elected the head of a multi-national organisation, a mentor of mine scolded me. “Do you really think that public speaking is about winning speaking contests?” she asked.

“Not any more,” I replied, chastened.

“This is what speaking is for,” she said. “You are leading a large organisation. This is the most important speaking opportunity of your life.”

She was right. That year we emerged from a 10-year slump. We didn’t break all the records, but we did grow by over 12% in a single year. It was the single best year since the 1990s all those years ago, when I was starting out in my leadership journey. And I can trace it back to messages I gave in different speeches, over and over again. Speeches that articulated a vision. Speeches that got 2,500 people to buy into a different future, and then make that future happen. Through myself and others, I was achieving a vision.

I always say it’s not called sell-in, it’s called buy-in. And how do you know that people have bought it? They sell it back to you. That’s when I knew I had succeeded. The leaders around me took that vision, they put their own spin on it, they re-articulated it for themselves and their own teams. They even sold that same message back to me. And they got things done.

In the intervening years I’ve coached executives and entrepreneurs and even a few contest winners. I’ve seen messages succeed and fail on the strength of how those messages are framed and communicated.

We tend to think of public speaking as a “soft skill.” It’s not. Getting people to take action is the hardest thing to do. And the secret to doing it at all starts with Michael T. Williams’ definition of leadership: “Articulate a vision.” If you can do that, and only if you can do that, will you be able to see your vision become a reality.