Every few years the same piece of technology gets re-announced, and it’s as important as ever. The feature? Undo. Its appearance marks a markets’ phase transition from early adopters to mega-profits.

Back in 1982 Norton Utilities launched its “Unerase” product. It was for the just-released IBM personal computers whose MS-DOS software was primitive and prone to data disasters. With an unerase, however, a user could, magically and for the first time, recover a file that they had accidentally deleted. It was a big deal.

Undo was new again a few years later. In 1986, Lotus Development Corporation announced the latest version of its (at the time) wildly popular 1-2-3 spreadsheet, one that now sported a spiffy new “undo” feature. If you made a mistake in your spreadsheet you could roll it back, a must-have feature for companies wanting to use PC spreadsheets (which still had “toy” reputations) for real business.

And now, undo is new yet again. A year ago, Google announced an “undo” feature for its Gmail product, allowing you to, for a few seconds anyway, abort an email that you just sent. And earlier this month Google announced “undo” for changes to its Contacts web service. Accidentally deleted the name of a key sales prospect? Bam, it’s back.

While it’s always nice to have a new feature, undo’s undue importance is much larger than merely allowing vendors to check some box on a feature checklist. Why? Because early adopters are used to products that break. They mostly don’t care about being able to step back from the brink — that’s the price they pay for being early adopters. The mainstream has money and risks, and so it cares immensely. It wants products and services where big failures aren’t catastrophic, and where small failures, the sorts of thing that “undo” fixes, can be rolled back. Undo matters, in other words, because its appearance almost always signals that a market has gone from fringe to mainstream, with profits set to follow.

If we listen to “undo”, what is it telling us now? It’s telling us that software as a service just blinked into being mainstream in 2010. Undo says the profits are about to roll in.

Paul Kedrosky is an investor, entrepreneur, and a senior fellow at the Kauffman Foundation.