The great Tom Chi taught me this lesson the other day when we both mentored at the Nike Girl Effect Accelerator:
A common mistake entrepreneurs make is to think and operate in conjectures. We base our actions on assumptions — we tell ourselves the story that customer X will do Y when we offer Z and then base all our actions on this assumption without properly testing it. We build products on assumptions. We create our business plan on assumptions. If we are good we raise money on assumptions. And when we find out (as so often) that our assumptions were wrong we change course — the celebrated pivot. Sadly, by that time, we have often burned through heaps of capital and many of us will never get to that pivot in the first place, as we simply ran out of cash.
What you want to do instead is to base your plans on actuals. Cold, hard facts. Things you can actually find out by rapidly prototyping your solutions. By getting out there and testing your assumptions dozens of times a day.
Facts trump assumptions any time of day.