This whole "Billion Dollar Startup" thing is itself a bummer.
People intend to brag about "Unicorns" and "Billion Dollars" in terms of valuation, which is paper money; and how soon it can vanish, the latest example is Theranos.
The thrill is not building a billion dollar valuation startup, the thrill is in building a billion dollar sales startup.
Mind you, when I am talking about billion dollars sales startup, I am not talking about GMV, since "GMV is too 2015" !
Focus on building a billion dollar sales startup, and you may be able to do it without venture capital, but if you focus on building a billion dollar valuation startup, you may be never able to do it without VC.