This song has been my favorite since I heard it for the first time. It was used in a commercial some 5 years ago I guess.
From then on, I often wondered what the lyrics are all about. At first, I thought it was about insomnia because the chorus goes: I'm trying, I'm trying to sleep. But I can't, I can't. etc. Then I came to think the song was about shooting incidents, where a man with a gun shot people indiscriminately in a university or a shopping mall. This interpretation was mainly based on the latter part of the chorus: But I can't, but I can't, when you all have guns for hands, yeah. And it is shared with other Japanese lovers of the song.
But now I am coming to realize that this song is in fact about young people killing themselves with a gun. This interpretation is derived from a close analysis of the whole part of the lyrics. Moreover, it may be especially about suicide resulting from depression. To make the interpretation more plausible, it is shared by some native speakers of English.
In Japan, the fact more and more young men in the U.S. kill themselves by shooting nowadays is not so covered as shooting incidents. So, It is difficult for Japanese to make sense of this song in this way. I will write an entry about this song and the correct interpretation of it some day.