Marc Andreessen Co-Founder and General Partner Andreessen Horowitz, investor and Co- Founder Netscape
“[Former Benchmark Capital General Partner Andy] Rachleff’s Corollary of Startup Success: The only thing that matters is getting to product/market fit. Product/market fit means being in a good market with a product that can satisfy that market.
 Lots of startups fail before product/market fit ever happens. My contention, in fact, is that they fail because they never get to product/market fit.
[The] life of any startup can be divided into two parts: before product/market fit (call this "BPMF") and after product/market fit ("APMF").
When you are BPMF, focus obsessively on getting to product/market fit.
Do whatever is required to get to product/market fit. Including changing out people, rewriting your product, moving into a different market, telling customers no when you don't want to, telling customers yes when you don't want to, raising that fourth round of highly dilutive venture capital -- whatever is required.
When you get right down to it, you can ignore almost everything else.” Marc Andreessen, “The Pmarca Guide to Startups, part 4: The only thing that matters, June 25, 2007; http://web.archive.org/web/20070701074943/http://blog.pmarca.com/2007/06/the-pmarca-gu-2.html