These decisions are highly nuanced. Of course we use a lot of data to inform our decisions, but we also rely very heavily on iteration, research, testing, intuition and human empathy. Now, sometimes the designers who work on these products are called " data-driven ," which is a term that totally drives us bonkers. The fact is, it would be irresponsible of us not to rigorously test our designs when so many people are counting on us to get it right.