I learned this one the hard way, as I think most everyone does. 

We're entrepreneurs, and as such, we see problems as opportunity. We evaluate the competitors, total addressable market, risk etc., and then propose what in our minds is the perfect solution.

It's beautiful. It's a hammer. It's handle - so ergonomic, it's weight - balanced to perfection, its color - inspires accuracy and power. No one in their right mind would ever use one of the hammers that exist today over ours. This hammer- it's a no-brainer.  

We get ourselves pumped up, and after collecting "enough" data we go heads down to build "a thing." In no time, our obsession has shifted from being focused on a problem to being focused on our solution.

You see this all the time. How many entrepreneurs walk you through their sexy Product X demo, but then get squirrely once you ask them what problem they're actually solving? In their quest to build a great product they've become completely detached from a real problem. 

Be obsessed with helping people drive nails through wood, not building a hammer.