I agree. My own experience is that entrepreneurs tend to greatly underestimate the difficulty of selling. Particularly on this forum, we talk a lot about "making something people want" as if that's all it takes for a startup to succeed but we don't talk enough about "making customers pay for what they receive". My own experience is limited to selling to enterprise customers. In that case, the necessary condition is to provide a solution that puts out a fire that is burning someone's butt. But it is far from sufficient. In the end, it all comes down to convincing someone to risk their career and the financial future of their family on an unproven product from an unproven startup. Having a killer product is only the first step.