What is the reason for not being able to sleep all the time

Is it really true that people who are often sleep deprived and feel fatigue and weakness are only like this because of the coming of winter and March? I think it is probably not the case, but what is

What is the reason for not getting enough sleep

Generally speaking, people keep about eight hours of sleep a day to ensure that the next day there is plenty of energy to study or work, but some people always feel sleep is not enough, so what is the