IF

A girl overslept and was 10 minutes late than usual.She took a quick shower, grabbed her bag and rushed out of the house.

A boy woke up as usual. He took his shower, had his breakfast and left the house for class. While he was walking towards the elevator, he saw the girl next door clumsily locking the door. He supposed that she was late for the class. So he purposely took another 3 minutes to wait for the girl to enter the elevator.

The girl dropped her books while locking the door, which took her 1 minute to picked up the mess .When she ran for the elevator she was surprised that the boy actually waited for her. She was so grateful towards the boy. The clock was tickling. She knew she wouldn't have overslept and was so regret. When she reached the building she managed to get the elevator just upon her arrival. She hoped in. When the elevator is about to shut, she saw a bunch of students rushing towards the elevator. That day the girl wasn't late for class.

However, if the boy decided not to wait for another 3 minutes. The girl would have to wait for another elevator which took another 5 minutes. And when she reached the building she would have just missed the elevator and have to wait for another 10 minutes for the cramped-up elevator.The girl would have late for class and being warned by the lecturer. She will end up having a bad day.

Conclusion:3 minutes wouldn't be too much, but it might change others' day.

Thank you, the boy next door!