“If you want a great site, you’ve got to test. After you’ve worked on a site for even a few weeks, you can’t see it freshly anymore. You know too much. The only way to find out if it really works is to test it.” —Steve Krug

Steve Krug's thoughts apply just as well to design as too much of life in general. Humans are designed to look for variety, and we very quickly grow accustomed to whatever we consistently experience. The best thing we can do is recognize this, and continually seek fresh perspectives on familiar problems.