(Flickr user The Marmot on a Creative Commons license)

Last April, Kraft announced that it would eventually change its famous macaroni and cheese. The plan was to get rid of artificial preservatives and replace artificial dyes with a trio of spices: paprika, annatto and turmeric. But there was no timetable — at least none shared publicly.

Now, almost a year later, it's clear that that was all an extremely calculated move on Kraft's part.

In December, the company's new Macaroni & Cheese Dinner quietly hit supermarket shelves, without a peep about the change. The boxes were lapped up, as usual. And why not? It would have taken a pretty astute shopper to notice the difference.

Kraft, which didn't bring attention to the new formula until two weeks ago, boasted about the little stunt in its first commercial:

For the past three months, we've been quietly selling Kraft Macaroni & Cheese with no artificial flavors, preservatives, or dyes. And guess what? Moms didn't notice. Kids didn't notice. Dogs didn't notice ...

"We’ve sold well over 50 million boxes with essentially no one noticing," Greg Guidotti, vice president for meal solutions at Kraft Heinz, told the New York Times.

The truth is that to call Kraft's maneuver a stunt is to do the campaign a great disservice. Letting everyone get acquainted with the new and improved product without anyone knowing that they were getting acquainted with a new and improved product is a stroke of marketing genius, a clever antidote to a problem many other companies have failed to overcome.

Introducing a tweak to something people already love is a tricky business. Especially when that thing is as iconic as Kraft Macaroni & Cheese. When people know a product well and adore it, they expect something very specific from it. They want it just as it is. They don't want it to change.

Perhaps the best example of this tension came in 1985, when Coca-Cola told everyone that it was rolling out a new and improved version of Coke. The new formula, the company said, was going to be sweeter and smoother and even more loved. But when the product hit shelves, people revolted. No one wanted this new thing. They wanted the old thing, the thing they had fallen in love with—they wanted Coke.

The problem wasn't necessarily that people didn't like the new product. It might have been. But it might also have been that they were expecting something different, because they had been told it would be different. And something different is not what they wanted.

That is precisely what Kraft realized.

Announcing that the new mac and cheese everyone was eating was different might lead people either to notice that it was different and to decide on those grounds alone that it was not good (or at least not better), or to imagine that it tasted different simply because they were prompted to.

So Kraft didn't, instead letting families — and broke college kids — form a new relationship without even knowing it.