Designers should be able to look at things and answer a simple question: why?
Of course, we’re interested in how things work. We’re interested in what they look like. We’re interested in when and where they are effective. We’re interested in who uses them. Al of these things help us understand what we’re designing.
If we focus on the why of why things work, those other things naturally follow suit. If we’re stuck trying figure out what something needs to looks like, we’ll miss out on everything else that makes a product great.