It's a bit different with pre-sale/aquisition than mountaineering, with enough money and therefore ability to hire talent it's not impossible to refactor/split the project or even rewrite as needed once the business value is established. Reddit did it, going from lisp to Python, as did Twitter with microservices, Facebook rewriting a PHP VM, etc.

Startups in your analogy are more akin to: "get to the mountain top and succeed and have the cash to hire a helicopter out of there, or you die (the company)".