Songfacts®:

• This punchy and melodic six-minute track was released as the first single from Dream Theater's eponymous 12th studio album. Guitarist John Petrucci explained why they decided to make this the progressive metal band's first self-titled record. "I see every new album as an opportunity to start over," he said, "to either build or improve upon a direction that has been evolving over time or to completely break new ground. This is the first self-titled album of our career, and there is nothing I can think of that makes a statement of musical and creative identity stronger than that. We've fully explored all of the elements that make us unique, from the epic and intense to the atmospheric and cinematic."
• Petrucci discussed the song with MusicRadar: "'The Enemy Inside' is a great example of a song that hits you, it doesn't meander, and it has all of the compositional elements that make us unique," he said. "It has the metal parts, the prog parts, the solos, interludes, choruses – it's all there, but in a more concise way that packs a powerful punch."
  
  "I wanted to write a fast-moving song on the seven-string with a big riff, a huge chorus and really fast, angular movements," Petrucci continued. "The irony is that we never intended for it to be a single, but it just kind of hooked everybody from the beginning. I always thought it would be a deeper cut on the album, more technical and fast, sort of a Panic Attack vibe. But it just turned out to be really catchy."
• Asked by Ultimate-Guitar.com to define the kind of guitar sound he was going for on this track, Petrucci replied: "I describe it as a piece of chocolate cake and that was my goal in the studio. It's like I had a nice picture of a layered chocolate cake. Why chocolate cake? Well, chocolate cake is rich, creamy and it has layers. It's sweet but it has a lot of substance and has just the right amount of icing on the top. If you get this nice piece of chocolate cake there's nothing more satisfying than that. So I wanted that in a guitar sound - a chunky, rich, delicious sound (laughs)."
• Petrucci told MusicRadar regarding his guitar solo: "There's a bunch of different parts to the solo. I try to always keep it interesting, and I want everything to have a musical purpose. The solo comes in a little late; it goes right into the final chorus. It was sort of my job to come out of the previous vocal and get us to the end."
• The song's music video was directed by Bill Fishman (the Ramones, Steve Ray Vaughan). The conceptual clip deals with the torment of a soldier who's struggling with reintegrating into his life back home due to post-traumatic stress disorder (PTSD). Petrucci told Billboard magazine the PTSD subject matter seemed to really fit the song since it's fast-paced and has "kind of machine gun riffs. It almost makes you feel anxious."
  
  He added: "Also at the time that we were in the studio working on the album and I was writing lyrics, the Boston Marathon bombings happened. There was a lot of discussion of terrorism and PTSD as if affects people who witness traumatic events like terrorism, so it was just very on my mind. It linked very well with the mood of the song, and as we started to get into it, I watched some documentaries and things like that. I was like, 'This is really something that needs to be written about.'"