For years you take the train to work every day, at the same time. But you began to notice, that, recently the train has been late a lot. You begin to wonder whe

For years you take the train to work every day, at the same time. But you began to notice, that, recently the train has been late a lot. You begin to wonder whether this is due to some change to the train infrastructure. But behind you someone shouts “the train was 10 minutes late on one day 20 years ago”. Do you dismiss your hypothesis?