Because everyone's first twenty years are basically spent in their study career. It is a process of mutual progress, mutual encouragement and mutual growth with classmates.
I have experienced a lot along the way. Perhaps the most touching thing is a pot of boiling water on a cold winter night, a bowl of instant noodles when you are hungry, or an umbrella when it rains.
However, for a large part of people, classmates have time constraints. After six years of primary school, three years of junior high school or four years of college, students will become weak because they don't contact and meet each other slowly.
Only in the process of learning, some close friends will break through the limitation of school time and continue the love of classmates into lifelong friendship or love. Classmates' love is emotional.