What's one thing you wish you knew before visiting Korea?

Looking back, what's one thing you wish someone had told you before your first trip to Korea?

For me, it was how useful Naver Map and Kakao Map are compared to Google Maps. I probably would've saved a lot of time if I'd known that beforehand.

It could be anything—transportation, food, payment, etiquette, apps, shopping, or just something that surprised you.

I'd love to hear what everyone else's was.