Summary: Users spend most of their time on other websites, so they expect your site to work like all the other sites they already know. When a design deviates from users’ expectations, usability suffers. Don’t be arrogant and assume that your new design idea is so brilliant that it can overrule decades of user habituation.
Jakob’s Law of the Internet User Experience
Is there a resource or spiffy rule of thumb, for deciding what areas actually need research versus copying conventions?