Excel wizards - what is the one formula that took you to scream: "Holy sh*t, where have you been all my life?

I just had one of those moments when I discovered XLOOKUP does partial matches and my jaw would drop thinking about all the hours wasted on nested IF statements. Which made me curious to know what other game-changers people have stumbled upon!

What's yours? Let's help each other level up our Excel game! Noobie here.