From idea to first paying customer — what was your biggest lesson?

I've been building products for 8 years now, and I've made almost every mistake in the book. But if I had to pick the ONE lesson that would have saved me the most time and money, it's this: **Talk to customers before you build anything.** I spent 6 months building a SaaS product that I was convinced people needed. I had a beautiful UI, solid backend, and a feature list that I thought was perfect. Then I launched and... crickets. Not because the product was bad, but because I had built what I *thought* people wanted, not what they actually needed. The second time around, I spent 3 weeks doing customer discovery interviews before writing a single line of code. I found out that the problem I was solving was real, but the solution I had in mind was completely wrong. The actual solution was 10x simpler and took 2 weeks to build. What was YOUR biggest lesson going from idea to first paying customer? I'm especially curious about: - How did you validate before building? - How did you find your first customers? - What would you do differently?