Gaining Buy in for Early UX Testing

Resistance to user-testing, especially user-testing very early in product development, remains rampant.

A lot of designers, engineers, builders, etc. trust their gut when it comes to how customers, users, and markets will respond to what they want to build.

They don't want to user test with wire frames and bare-bones prototypes and can't imagine iterating to something better than what they've imagined. They just want to build because they already just know what they should build.

How do you overcome this resistance? How do you get them to buy into the value of early UX testing?