A night is part of a day. Every night we wish our loved ones to have a good sleep. Good Night is a phrase, used to greet people at night times. Also, it can be like waving off or a sign to sleep. Generally, we follow the culture of sleeping at night times and working at day times. While we wish people to sleep with a hope that tomorrow is going to be a good day.
As it is the end of the day, people go to sleep peacefully. Also, Night is to see dreams and day is to make them true. Usually, we go to bed by thinking all the memories of that day. But the correct way is to think all good memories which increase positivity.