"After his poor performance at Worlds 2013... Since then, he has been an OGN finalist twice, won another Championship and an MVP as well as an OGN Masters Championship."
He also was the 2013 Spring Season MVP and highest KDA of mid laners...
2013 Spring... y'know, BEFORE the Season 3 World Championships, where he absolutely wet the bed. I'm still busy counting the amount of missed Gragas ults in that game against Fnatic. Yes, he was statistically the best mid laner in Korea for a period before last year's Worlds, and completely choked when the lights were at their brightest.
Winning OGN is one thing, when it's mostly only Koreans watching. Playing at Worlds, the pressure is entirely different, especially when you need to perform in front of your own country's fans, or face the ridicule of a ravage internet fanbase for losing to a foreign country (assuming he doesn't lose to another Korean team).
TL;DR He's already choked on the highest stage possible after being named a Korean MVP. Who's to say he won't choke again this time, especially when his group counterparts consist of XiaoWeiXiao, xPeke, and Cool?