“People are really nice — some can just pay you, even for a non-existing product. But you still don't know if they'll use it… Once you have at least 10 paying customers from outside your network… that's, for me, the ultimate validation.”

Ten paying strangers from outside your network is the only real validation

Friendly opinions and even pre-orders from your network aren't proof anyone really wants the product. The real validation bar is ten paying customers from outside your network who found the product themselves and stuck around to use it.