(CNN) There's a very odd -- and telling -- moment in President Donald Trump's interview with The Economist released Thursday morning. Here it is :

TRUMP: We have to prime the pump.

ECONOMIST: It's very Keynesian.

TRUMP: We're the highest-taxed nation in the world. Have you heard that expression before, for this particular type of an event?

ECONOMIST: Priming the pump?

TRUMP: Yeah, have you heard it?

ECONOMIST: Yes.

TRUMP: Have you heard that expression used before? Because I haven't heard it. I mean, I just...I came up with it a couple of days ago and I thought it was good. It's what you have to do.

Trump, quite clearly, believes he came up with the phrase "prime the pump." Or at least that he is the first person to use it in regards the potential kick-starting effect of tax cuts on an economy.

A simple slip of the tongue by Trump? I don't think so.

Here's the thing with Trump: He is someone who has always created his own version of events and reality. One of his tried and true tactics as a businessman was, no matter the outcome of a deal, to declare victory and move on. He would aim to win the next day's press story -- knowing that for lots of people not paying close attention that would be all they would hear.

And he didn't stop doing it once he became a candidate for president. He would simply say things -- Muslims were celebrating on the roofs in northern New Jersey after 9/11, Ted Cruz's father might have been involved in JFK's assassination (or maybe he wasn't!), all the polls showed him beating Hillary Clinton -- that weren't factually true but seemed right to him. His gut -- the much-ballyhooed origin of most of Trump's political instincts -- told him this stuff was right, so who were fact checkers and biased media types to tell him -- or his supporters -- differently?

Trump kept building his own world once in the White House. He would have won the popular vote except for the 3 to 5 million votes cast by undocumented immigrants. His inauguration crowd was the biggest ever. His first 100 days were among the most successful of any president ever. And so on and on and on.

It didn't matter that all of these things were provably false. What mattered (and matters) is that Trump believed them. That made them truth to him.

Which brings us back to him inventing the phrase "prime the pump." Of course he didn't do that. But Trump came up with it in relation to his tax reform plan -- raising the deficit in the near term via tax cuts in the belief they will "prime the pump" for future economic growth -- so he, naturally, believed he was the first one to think it up.

That takes some significant self-regard. But also a sense that if you say it, it must be new and true. And Donald Trump believes that whatever he says is, by definition, new and true.