Tell me about that one ingredient, that when discovered, it opened your mind to a whole new world of flavor possibilities!
For me, the first to come to mind is Worcestershire sauce. I'm talking about way back in my youth. It was my first introduction to what we now call umami. When I noticed my mom put it in her meatloaf I began experimenting. At the time I was just blown away by how much it changed things. I even used to put it in my Top Ramen I was so obsessed lol. More recently, dukkah. Trader Joe's is correct when they say to take bread, dip it in olive oil, and then dukkah. So tasty!!
It's basically the same for me! I'd say anchovies/fish sauce in general. My first introduction was through Thai fish sauce, which I grew up with and learned how to use in Thai cooking. Then, I started cooking with anchovies in oil and Worcestershire sauce in what I viewed as their respective cuisines. At some point I understood the similar role these ingredients played in providing the umami element needed to complete a dish, and that made me feel more confident using them in a wider variety of foods and "across" cuisines as needed. Used in the appropriate amount, they won't overpower a dish or turn it fishy; a little bit provides so much flavor!