Share your "failures" and how that also become your biggest asset

I'll start. I started my first company when I was still in University, at the time I was in the "Rapid Delivery" space, delivering grocery in 15 minutes to local students. We got some great tractions, but we never made a profit, and had the hope that it'll be profitable when we scale. However, we soon realized it's a business that will never make a profit, and we were just chasing the trend of "Rapid Delivery". We saw it was hot in Europe, that's why we did it in Canada. It turns out that no players survived in this rapid delivery space. Billions of VC dollar all went down the drain... This taught me a few important lesson, before we are a start-up, we have to be a business, that have solid business fundamental, then we can consider how to grow fast. Second is to not follow the trend, you never know what started the trend, and whether the trend will be a fad. Just follow what you're truly interested in or believe in. Thanks for reading, what's some "failures" that taught you a big lesson?