What was your biggest failure and what did you learn from it?

if I can't remember failure, am I a narcissist?

My biggest failure was my spontaneous t-shirt business. At 6'2", most t-shirts are too short and begin to look like crop tops after one wash. With zero manufacturing experience, I branded and sold 10 shirts after the first hour of launch. I had to refund everyone because I couldn't make the t-shirts. But the real failure was my friend's involvement. After I launched my friend joined and she didn't see the vision, so we planned, pivoted, repeat without actual action. We became something so different at the end, what started as a way to solve a personal problem (t-shirts for tall people), morphed into high-end evening wear for women (which we never actually launched). The Lesson: Choose your team wisely, act more, overplan less.