Product design is about function.
This is something many companies get wrong — they attempt to answer how it looks over how it works.
Physical or digital, the principle prevails.
How many clicks or taps does it take for someone to accomplish their goal in your app? Why are there three ways to get something done instead of just one? What limitations are in place (and are they necessary)?
That is function. That is how it works. That is true design.
"Design must be functional, and functionality must be translated into visual aesthetics without any reliance on gimmicks that have to be explained." Ferdinand Porsche
This extends to how something feels. After all, you're not selling the product itself, you're selling an emotion — a means to an end.
People don't buy Hermes handbags because they need an absurdly durable carrier for their wallet and keys. They're buying their way into a higher social status and whatever emotion that brings to them.
The problem is different people buy your product for different reasons. Harry spent half his savings on a highly-regarded home security system so he and his family could feel safe — at peace. Sally bought your new super-food oatmeal so she could feel healthy — worthy of that chocolate bar later on.
But that in itself is a great reason to establish a real niche before you start designing. You won't know how something should look, work and feel without knowing who it's for.