The 3 W's of Business:
What - is the problem you are solving?
Who - is the customer that needs this?
Where - are they so you can market to them?
That's it.
I was at Amzn early '00s when we lost 95% of our market cap. Later at FB I negotiated a down-round in '09, and then in '12 our stock dropped 50% post-IPO. I was on the board of a public company that went bankrupt (Borders) and a start-up that went under (Hello). Some lessons: