Giving up 80% for "an idea" is fine. Giving up 80% for the first customer? That's a big ask. Someone noteworthy said that 50% of building a business is going

Giving up 80% for "an idea" is fine. Giving up 80% for the first customer? That's a big ask. Someone noteworthy said that 50% of building a business is going from 0 to 1 customer. The other half is going from 1 to many customers. That being said, this person is assuming a lot of risk that the partner is flaky and doesn't follow through, that financing won't be available, etc etc. In reality, I suspect they're probably building out a 4-6 week MVP, getting a couple of customers, then selling the business as a "turnkey startup" for ~$50k (of which they get 80%/$40k). Not a bad proposition.