New here - long-term value investor, burnt by a single concentrated bet early on

Hey everyone, just joined. Been in the markets for about 15 years now, mostly focusing on value investing and long-term holds. My biggest lesson came early, holding way too much of one small-cap stock. Thought I had a deep understanding of the business, but when the market turned on it, my portfolio got absolutely clobbered. It taught me the hard way about true diversification and position sizing, even if you're convinced you've found the next big thing.