Lee Joon discussed his difficulties with acting with an interview with Herald POP. 

The actor shared, "I used to think like this -- all the idols are now acting, but I am not getting parts even though I want to act, and I am asking to be cast. Honestly, after 'Ninja Assassin,' I had a lot of confidence. I thought I should be able to do a lot of acting gigs from that point. I had good reviews from the movie, and I was happy. However, I couldn't do any acting for years." 

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After he started acting more, there were still difficulties. In films like 'Customer' and 'Lucky,' his parts would get edited out a lot. However, Lee Joon stated, "I didn't get hurt from that. It's for the whole movie, and editing is expected if I don't do a good job. I am just thankful that they let me be in the movie. I don't get offended by editing." 

He added, "Many people said that my parts in 'Lucky' were boring after seeing the movie. I was worried and became a little less confident." But he laughed and added, "But it's okay because it's not like I didn't put in the effort." He explained that he did not want to overshadow the main role who is the funny character. Lee Joon stated, "I did everything I could. But if viewers say that I am boring, then I must own up to it. I'm rather sorry to the viewers, and I want to try harder to get better." 

Lee Joon also added, "The movie itself, I enjoyed...Personally, I liked it. Because I was in it, I wasn't bored," while laughing. He continued, "I can watch a close-up of me for 1 hour without getting bored, but if the movie watchers say it was boring, then it is. If I deny it, there will be no growth."