Tokyo is a big city and many people live around Tokyo. Also many companies are located in the center of Tokyo.
Therefore, almost people commute to the offices by trains. A lot of trains and subways run in Tokyo. At rush hour in the morning trains are very crammed with a lot of people.It is symbolic scene in Tokyo. After they get it off, it is as if the station is flooded with the wave of people. And other countries people will be surprised at this cram and a flood of people.There are some people who get on for 1 hour or more than 1 hour to commute. The cram is sometimes like a hell. I get on these crammed trains every morning.
Interval of time schedule is so tight. The interval for Yamanote line is 2 or 3 minutes. Time is almost accurate. It is remarkable. The congested time schedule might be a reason that everyone says Japanese seems to be always busy . This is typical system for Japan.