They drive on the left side because they walk on the left side. They say the origin for left-hand traffic in Japan comes from the Edo period where samurai, who wore their swords on the left side, would walk on the left side of the road to avoid clashing swords with each other.

Left hand side vs right hand side has a really complicated history. A lot of Europe was left hand side first as well, although I just learned from Wikipedia that that might be myth:

https://en.m.wikipedia.org/wiki/Left-_and_right-hand_traffic

It depends...

60-Hz AC in Osaka and 50 Hz in Tokyo. Standing on the left of the escalator in Tokyo and on the right in Osaka. Oh Japan..

https://www.japantimes.co.jp/news/2011/07/19/reference/japan...

https://kotaku.com/its-hard-for-japan-to-change-its-escalato...

Japanese sidewalls are rather paradoxical: where rules and order are so valued, pedestrians are in chaos. People walk 4 abreast, walk in bicycle lanes, randomly change direction without looking etc.

Escalators are even stranger. There are signs everywhere telling people to stand on both sides. These are completely ignoreed. People fill up one side completely and leave the other side empty for the occasional walker.

^ This guy has really been in Japan! There is no standard of walking on the left or the right. People don't follow vehicle driving protocols because many of them never have or will drive. "Paradoxical" is absolutely the best way to describe Japanese pedestrian behavior.

The escalator one depends on how busy it is. During rush hour or when the line at the "entrance" begins to grow longer the free side gets a lot more traffic, though usually people will still try to walk on that side in order to not block the "fast lane".

Many people in Japan don't drive so they don't really think about "sides" like people who come from car cultures do.

I didn't say anything about cars and as Hamuko has pointed out, it predates cars. Wikipedia supports this claim, though doesn't cite it.

Interesting! That’s a bit surprising to me. In Japan they have the yellow tiles with bumps near the center of most city sidewalks that I always assumed was a kind of lane system. If it’s not to create lanes, what are those tiles for?

They are tactile paving for blind and partially sighted people.

https://en.m.wikipedia.org/wiki/Tactile_paving

Lanes for the blind.

This. As a driver and a long-term resident in Tokyo, I try to stay to the left as a pedestrian, but I estimate the odds of the other party doing the same are 50/50.

Yeah, and you also see people being paid to direct the flow of human traffic at the super busy stations.

They come in contact with it though, from those driving around them. Then there are other customs, like standing on the left side of escalators (except for Osaka, where it used to be the right side, but now it's mostly the side the line is already on). From my personal experience people in the major cities seem to prefer dodging to the left, all things being equal.