Essentially, this song is describing multiple things related to the concept of a sudden and unforeseeable love. The first line "I guess I act too quickly" refers to how this is a rash and instinctive decision that is recognized by the artist. The next line "I'm probably a fool" shows that the artist is afraid of being rejected as shown by how the next lines (in which the artist doubts themself) by asking; "Should I have taken one more breath and try and keep my cool". The infliction in the next line also adds an emphasis with the half-step up on the word "enough" referring to how he a) wants to spend more time with her and b) does't have the words/time to convey his emotions for her. Moving on to the chorus, "It happened in a moment, nobody gave a cue" these lines refer to how it was a spontaneous action that wasn't planned out or expected. The next lines "One look into your brown eyes, I knew it was you, I knew it was you [extended]", refer to the fact that it was a certainty, one without question and ignorance that left no room for doubt. These lines are followed by "It's like a perfect casting, you're born to play the part, there's no going back now, you've taken my heart". In essence, this quatrain is referring to the fact that she was the perfect match for the artist and and creates a metaphor illustrating as such. The next lines are the same as the first five lines, yet the final three lines (or two) sum up the piece quite nicely. "When your the one and only thing that I am thinking of" demonstrates that the artists love for her is all consuming and beautiful.