Ron Garret lists out 10 myths. Among them:
Myth #2: If you build it they will come.
There is a grain of truth to this myth. There have been examples of businesses that just built a product, cast it upon the ether(net), and achieved success. (Google is the canonical example.) But for every Google there are ten examples of companies that had killer products that didn’t sell for one reason or another.
Myth #5: Financial models are bogus.
As with myth #2 there is a grain of truth here. As Carl Sagan was fond of saying, prophecy is a lost art. There is no way to know for sure how much money your business is going to make, or how much it will cost to get to market. The reason for doing financial models is to do a reality check and convince yourself that making a return on investment is even a plausible possibility. If you run the numbers and find out that in order to reach break-even you need a customer base that is ten times larger than the currently known market for your product then you should probably rethink things. As Dwight Eisenhower said: plans are useless, but planning is indispensible.