TOKYO - Trains in Japan are well-known for their punctuality. But on Tuesday (Nov 14), a train on the Tsukuba Express line in Tokyo failed to stick to its timetable - by leaving 20 seconds early, reported Japan Today, citing SoraNews24.

The incident prompted the train management company to issue an official apology on its website later in the day: "We deeply apologise for the severe inconvenience imposed upon our customers."

The Tsukuba Express line, run by the Tokyo-area Metropolitan Intercity Railway Company, connects Akihabara in Tokyo with Tsukuba in Ibaraki Prefecture.

According to the report, a north-bound train leaves Minami Nagareyama Station at 9.44am on regular weekday mornings. However, on that day, the train left at 9:43:40 instead, 20 seconds earlier than it was scheduled to.

With trains coming every four minutes on the Tsukuba Express line in the morning, it is doubted that a 20-second difference would be noticed by people, Japan Today said.

However, as Japanese trains are usually punctual, some people plan their rail commutes precisely to a tee. In other words, by missing the train and adding four minutes to another leg of their commute might cause them to miss other transfers on the way to their destinations, with the effect snowballing enough that they end up being late for work or school, according to Japan Today.