The mysterious art of proving that real customers will want to buy your product, before it even exists.
Techniques include: purchase ads and see if they click through to the purchase option. Kickstarter campaign to generate seed capital.
Instead of trying to prove your idea is valid, you should try to prove your idea is invalid. But you'll only be willing to do that if you're not already attached to your precious idea.
My book "Choose Your First Product" is available now.
It gives you 4 easy steps to find and validate a humble product idea.