they greatly underestimate the interface work as well.

And, oh boy, the word operations is not even mentioned. Bringing your prototype to the customer is one thing, but actually operating it can be as challenging as developing it.

Of course you can outsource a great deal of that to AWS/Azure/gcloud nowadays but either way you’ll have to throw a significant amount of money (and manpower) at a problem the non-techs probably classified as trivial.

I wouldn’t want to be the only techie, being on call 24/7 for the next 3-6 month until that project finally runs out of money. As interest rates are high now, loans aren’t an option. Getting eaten by a bigger fish is also unlikely, so you better generate a proper income for everyone involved asap. You can bet on such a thing to work out if you’re still young and have a safety net (i.e. parents). Unless you’re running an operation, you invest either money or time, never both.