What’s one ingredient you started using that completely changed your cooking?

I love trying new recipes, but I’ve realized it’s often the smallest ingredients that make the biggest difference.
For me, discovering how much freshly squeezed lemon can brighten up a dish was a game changer. It’s such a simple thing, but it makes so many meals taste fresher.
I’m curious—what’s one ingredient, seasoning, or pantry staple that completely changed the way you cook?
I’d love to discover something new to try this week.