Who's the audience?

Jakob Nielsen's latest Alertbox says:

One of usability's most hard-earned lessons is that "you are not the user." If you work on a development project, you're atypical by definition. Design to optimize the user experience for outsiders, not insiders.

But 37signals says we should design products that we use ourselves, not do user testing, and "iterate in the wild."

They're both quite successful; but can they both be right?

The "real" answer is that there aren't any hard and fast rules, and no magic wand you can wave to build a successful website -- every project's going to have its own requirements and pitfalls to avoid. But at the end of the day (to use a Trump-ism), we can all agree that what's important is building a product that works, and making the experience of using it as pain-free as possible.