Unlike other nations in Asia, the Japanese have no custom of tipping for good service, and no matter how good a particular customer experience was (or wasn’t), you’re never expected to leave a tip. In fact, doing so would probably result in the server in question chasing after you to return the cash you accidentally left on the table. Still, Japanese know that tipping exists in the rest of the world, and part of preparing for a journey abroad involves studying up on how and when to leave a gratuity. When an American eats at a restaurant, he’ll probably toss a couple dollars onto the table when he leaves, perhaps rounding up if the service was especially good. But Japanese are likely to meticulously calculate the correct 15% tip for the meal they just ate, counting out the coins on the table. I’ve lived in Japan long enough that some of this nervousness about tipping has spilled over to me, and I found myself putting a few $1 bills in my pocket so I could hand it to people who helped me with my bags at the airport, etc.
Living in Japan will make you worry about tipping like the Japanese do.