The assumption is that this is the case because tiredness sets in, but that is not 100% true.
Do you remember the story of the tortoise and the hare? The hare felt like the job was done as he had made considerable progress compared to the tortoise. That sense of accomplishment made him relax before completing the race, he eventually lost.
I read a statistic that most car accidents occur within a few kilometres of people’s homes, the conclusion of the report was that people tend to relax when they are getting home and this impairs their judgment as they are not as vigilant as they should be.
You can’t afford to turn off when you are close to the end, when you are almost there, when you are at the last mile. As they say, it’s not over until it’s over.