What’s the one Excel trick or formula that changed everything for you?

I feel like Excel is one of those tools where a single formula or shortcut can save hours of work.

For me, learning things like basic formulas and shortcuts already made a big difference, but I know there’s still a lot I don’t know.

So I’m curious:

What’s that one Excel trick, formula, or feature that made your work much easier or faster?

Could be something simple or advanced - anything that you think more people should know.