As the testing went on, it became evident that the key to making the Watch work was speed. An interaction could last only five seconds, 10 at most. They simplified some features and took others out entirely because they just couldn’t be done quickly enough. Lynch and team had to reengineer the Watch’s software twice before it was sufficiently fast.
It's becoming increasingly clear that Apple designed its new watch to be used as little as possible, with information to be glanced at rather than studied. As the piece points out, holding your arm in the air for any length of time is no fun at all.
Figuring out how to send a text was illuminating. Initially the process was a lot like texting on an iPhone: addressee here, message here, confirm message. Tap to send. “It was all very understandable, but using it took way too long,” Lynch says. Also, it hurt. Seriously: Try holding up your arm as if you’re looking at your watch. Now count to 30. It was the opposite of a good user experience. “We didn’t want people walking around and doing that,” Dye says.
The whole article is worth a read even if you only have a passing interest in the Apple Watch.