Your customer is president for life

Many promising startups fail to succeed after getting funded because they fall into an unexpected ditch. That is, they think the world has approved and validated their idea when it was only done by a handful of rich people.
The truth is, customer is king. The customers are the ones whose validation matters the most. In fact, part of the reason the investor is investing is so that you can have more financial power to sponsor more customer data gathering activities.
Funny enough, when that investor funds show up, everybody forgets the sorrows of life and start balling.
Brand new office, expensive chairs, mac book moons, developer events, speeches, charts, custom t-shirts, new cars, huge salaries and chieftaincy titles.

But guess what, everyone forgets the customer. 2 or 3 years later, that once amazing startup disappears back into oblivion where it came from, because the product became boring, useless or unusable.
You see, the customers are the ones that determine what nature of product to be built because they are the ones that pay for it.