it was his 18th birthday, it was the day he will be having a mark on his neck, showing people how long will he live; he woke up to become a normal teenager who hopes he lives until the day his mother dies; well, he thought so? 

he has a few other friends, people who loved dancing just like he does. but no one shows off how long they had to wooyoung. so wooyoung took it as they all will die next year. easy conclusion. he didn't care as much because "people come and leave". 

but secrets means something.