In an Vlive by RM, one of the members of BTS, he said:

“Begin” is a track that starts. It’s the beginning of the solo songs. It’s the story that our youngest member (Jungkook) is telling. Jungkook tried to write the lyrics by himself at first – It’s best to write your own lyrics. But Jungkook was really troubled with trying to write the lyrics, so he came to me. He wanted me to give it a try.

I felt a lot of pressure in the beginning. It’s Jungkook’s story, and I’m not Jungkook. Even if we are members [of the same group] and live together. “Can I talk about someone else’s story?” I wanted to tell Jungkook’s story as it is.

[…] In the beginning of this year (T/N: This live video was in 2017) we got together and cried. There was a dramatic moment where we got together honestly. Was it this year or the end of last year? That’s the first time he cried and talked about his feelings. It was my first time seeing him cry that much. The topic back then was what was painful for each of us. Jungkook said nothing was difficult for him – he signed the contract at a young age, knowing nothing. He sang and danced and worked hard since he wanted to. What pained him the most was the other members [of BTS] being in pain. We all cried. That was so sad. Jungkook never said anything like that before. He would always say that nothing was bothering him, “I’m okay, I’m very strong”. That’s how he was. It was my first time hearing Jungkook’s troubles. […] I don’t care about other things, I just don’t want you all to be in pain. Then I won’t be in pain too. That’s what he said. I remember that so much. It was so impressive, what he said back then.

Was it for the epilogue? I don’t remember. He said something similar at the end of the concert. […] So there was a video of him talking. I tried to think like Jungkook, watching that video. […] I’m thankful that Jungkook thought the lyrics were good.

There was a clear melody in this song. We got the melody from overseas. We can’t change the rhythm when translating to Korean. I wanted to tell you we had a bit of language difficulty.

“Begin” means a lot to Jungkook. I think it was the beginning of what we are now. […] That’s how “Begin” came to be. I hope next time Jungkook can write his own lyrics.