What life-changing skill do you wish you'd learned earlier?

I recently learned how to cook properly at 35, and it's been a game-changer. I'm saving money, eating healthier, and actually enjoying my meals. It got me thinking about other skills I wish I'd picked up sooner.

What's a skill you wish you had learned earlier in life? Something that's made a significant difference in your day-to-day living or overall happiness?