Rachleff's Law of Startup Success: When a great team meets a lousy market, market wins. When a lousy team meets a great market, market wins. When a great team meets a great market, something special happens.

Andreessen credits Andy Rachleff of Benchmark Capital for this formulation.

In a great market, the market pulls product out of the startup. The market needs to be fulfilled and will be fulfilled by the first viable product that comes along. The product doesn't need to be great; it just has to basically work.

You can always feel product/market fit when it's happening: customers buy as fast as you can make it, money piles up in the checking account, you're hiring support staff as fast as you can, and reporters are calling about your hot new thing. When it's not happening, word of mouth doesn't spread, sales cycles drag, and deals don't close.

When you are BPMF (before 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.

The classic counterexample to 'great product = success' is the world's best software application for an operating system nobody runs—just ask any developer who targeted BeOS, Amiga, OS/2, or NeXT. Product quality and market size are completely different things.

Once a startup is successful, founders cite all kinds of things that had nothing to do with it. People are terrible at understanding causation. But in almost every case, the cause was product/market fit. Because, really, what else could it possibly be?

The most frequent case of a great team paired with a bad product or terrible market is the second- or third-time entrepreneur whose first company was a huge success. People get cocky and slip up—Andreessen cites one high-profile founder burning $80M in venture funding with nothing to show because there's virtually no market for what he's building.