Facebook employees describe the challenges with naming the "Decline" button for Facebook Events:

“People hated clicking that,” says Matosich. “That’s the language of the button, that’s what goes out to the host. It spiders out: ‘So and so declined my event, did I do something wrong?'” When it came time for Facebook to revamp its events pages, the team considered a variety of possibilities to replace decline: No, Can’t Go, Not Going, No Thanks, and Unable to Go were among the options.

Eventually, Can’t Go was the chosen winner, because while Not Going is more literally accurate, the intent of Can’t Go is truer to what people want to communicate. “People don’t know how much care we put into this. It’s one little button, it’s one little option, but we want to think through all the use cases,” Matosich explains, saying the team testing the phrases across different UIs and scenarios (how it looked in different notification screens, and as a response to birthday parties, memorial services, book clubs). “We don’t believe in edge cases, we want to find something that works for everyone. We don’t want to alienate anyone or make anyone feel icky … we don’t want to put words in anyone’s mouth.”

When Facebook replaced “Decline” with “Can’t Go,” a funny thing happened: People actually started using it.

For graphic artists, every pixel matters. For sound engineers, every decibel matters. For web developers, every kilobyte matters.

For user experience designers, every word matters.