As readers of this column know, my company, 37signals, has been working on one of our most ambitious projects ever: a ground-up redesign of our signature product, Basecamp. An online collaboration and project-management tool, it has more than five million users, and it is our top-selling and most profitable product by far.

The redesign took about a year. And then, finally, on March 6 at 8 a.m., we hit the Launch button. We were live. By the end of the day, more than 10,000 new customers had signed up. We experienced no slowdowns, no downtime, and no disasters.

But I don't want to talk about what went right. I want to talk about one of the rough spots we hit, because it taught us an important lesson about customer psychology and how to manage expectations when introducing something new.

One of the things our designers and developers spent a lot of time on was a migration feature that would enable current Basecamp users to move their projects, data, and users to the new version. Our goal was to make sure that the transition was smooth and risk free.

Risk free it was. Smooth...not so much.

Let me back up for a moment. The new Basecamp differs considerably from its previous iteration (which is still available as Basecamp Classic). It does many of the same things but has a new interface and does those things differently. The new Basecamp is better, faster, and simpler. But it is different enough that it really feels like an entirely new product.

For the tens of thousands of new customers who signed up, that hasn't been a problem. But many longtime users had a different experience. For them, new didn't mean better. It meant different. And different is always a challenge.

For longtime customers, who rely on Basecamp to run their organizations, the upgrade was disorienting. I imagine it was like walking into your living room, only to find that someone had changed the wallpaper and rearranged the furniture. Figuring out whether it looks better or worse isn't the first reaction. The first reaction is, "Something has changed; this is different"-- a reaction that often leads directly to anxiety.

No business owner wants to make customers anxious. But that's what we did by enthusiastically encouraging existing users to try the new software, and by making it really easy for them to do so.

Here's what we learned: New ideas take time to get used to. Inviting people to change to the new Basecamp while they were in the middle of their long-running projects turned out not to be a very good idea. It kick-started anxiety. And customers weren't shy about letting us know.

Looking back, what we should have done was to invite existing customers to check out the new Basecamp without encouraging them to make a wholesale switch. Then, after they'd spent some time kicking the tires, they could decide what they wanted to do. As with so many business lessons, it seems obvious in retrospect, but entrepreneurs need to think as much about customer habits and expectations as they do about design, code, hardware, and the like.

Fortunately, our customers are awesome and understanding. Same with our service folks. With a little handholding, even the most baffled users were able to get the hang of the new software. We're getting a lot of "I wasn't sure at first, but now I love it" notes.