It's true that the excessive need for external validation kills many startups.

A pattern I've seen over and over (and I fell myself in that trap once) is:

A startup wants to disrupt an industry by making a self-served, SMB targeted product (think Zendesk). But they want external validation. Actually you can understand that: their bank account, their family, their ego want external validation. So they start reaching out to large enterprises. A few of these enterprises become customers and start to dictate the product roadmap. Soon enough, the startup has forgotten its self-served, SMB, disrupting vision and joined the ranks of the old-school vendors it wanted to disrupt.