Today Twitter CEO Evan Williams announced he would be stepping down as Twitter’s CEO. Dick Costolo, presently the firm’s COO, will take over that role.

As is its custom, Twitter (the site) exploded with the news, as geeks everywhere speculated, double rainbow-like, What does it mean?

The answer is that they’re simply tending to their business. The myth that founders somehow have mythical vision and deserve important sounding titles like CEO is really mostly garbage. Founders are mostly like everyone else, except for one important difference.

Founders try things. They seek new markets and ideas where others don’t. But they seldom have all the answers. Sometimes they are even visionary, but that doesn’t always make a good CEO from a day-to-day build-the-business standpoint.

Fact: Twitter was not Evan Williams’ idea. It was Jack Dorsey’s idea. And in fact Jack was CEO of the company from 2007 til late 2008 when Williams, a co-founder and early funder of Obvious Corp, took over. (Jack, a great guy and a big dreamer, went on to found Square.)

Fact: No one at Twitter had any idea where it might go when it was created. Seriously – neither Dorsey nor Williams predicted this outcome. I’ve talked to them both about it and the fact is they were just regular guys who tried something new. They had enough resources and drive to make sure it could grow, but they really had no idea where it might lead.

The whole idea that folks like Evan Williams, Jack Dorsey, Biz Stone, Mark Zuckerberg, or Kevin Rose are well-suited to actually run the businesses they have created is pretty much a myth. But yet it’s one people seem to like to believe.

Founders have a very different personality from the sort of person required to build, operate, and grow a business financially. The sooner we can all get over the celebrity CEO complex, the better off we’ll all be.

People need to understand exactly what it takes to found a startup, and Eric Ries has gone so far to say that entrepreneurs actively lie to promote the visionary founder myth – and I agree with him.

Costolo is a genius at building a new-media business like Twitter. Williams is a persistent guy who’s willing to break new ground.

Two. Different. People.