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It is the first song frontman Andrew McMahon wrote and recorded after his stem cell transplant in connection with his leukemia diagnosis in late 2005. The song's lyrics are heavily influenced by his recovery from the disease, indicated in lines like "I'm coming home from my hardest year" and "It's good to be alive".
References
"3 days in LA". Jack's Mannequin Blog. Retrieved November 26, 2005.