As we already know that Go Jun Hee gets Go yoo's skill and personality because of cellular memory syndrome. So it has the possibility that same happens with Go yoo; for example- he starts wearing glasses and leads a boring life with lots of books. That's why So Yeon was so surprised to see him as Go yoo was the fun type of person.
Dear @roddib, you've been replying to every comment like someone has hired you as Sehun's prosecutor LMAO! As you said about people's right to express their opinions, you should also let others express theirs!
(My prediction can be wrong though.)
(I've already read what you wrote before editing this one.)