How do you validate whether an idea is worth pursuing?

Get in front of ten customers or potential customers and do not pitch. Ask questions. Find out what pain they are experiencing, what they are excited about, what problems they would pay to have solved. Then try to make one of those ten people actually buy. If someone is willing to pay, that is real signal. Free is not signal. You need the friction of payment to know they actually care. Then hope that those first buyers spread the word. Make them feel special. The goal is to build a small group of people who love the product enough to tell other people about it, and then figure out how to scale that distribution from there.