This can be explained quite easily. In order for any business to succeed, a market has to really care about what your business is selling.  

The journey of starting and running your business...

So there you are, sitting in a coffee shop or out on a walk and that "million" dollar idea flashes before your eyes.  You are convinced that you have something special.  You wonder how no-one has ever thought of this before.  You begin to do plan your attack, do some research and find data to support your great idea. You are now 100% convinced that everyone will care about what you are selling.

Enter the first problem:

1) Confirmation Bias

When you are convinced of an idea, you only see what is in support of your idea.

Solution:

Write down, in detail, the target audience that would be the buyer of your great idea...then go find at least 30 people or companies that are a part of that audience and ask them if they find your idea interesting and if they would pay you money for it.

2) A Bootstrap Start

Assuming you pass step number 1, scrap together a minimum solution and launch, but spend no money on paid advertising.  You are only allowed to market utilizing extremely low cost or preferably no cost methods.  Now here comes the next great piece of feedback.  Does anyone actually buy what you are selling.  Now when I mean buy, I mean at full price...if you have to discount even $1 to sell what you are offering, then you are not solving a real serious problem that people or companies really care about.

3) Iterate or STOP

Assuming you pass step #2, now is the time to take in the objective market feedback that you just got and either make changes and try the loop again or STOP...your idea is not working.  There is nothing wrong with iterating, as long as you take in the feedback that you received.

This is advice from the trenches.  I am not just your average consultant.  I have started companies, raised millions of dollars, thought I knew everything...I wish I had someone to advise me, when I was in the early stages of my businesses.