The chorus, which thanks someone for "the best day of my life," refers to the night they first met at a club.
While her physical world is literally falling apart, the lyrics emphasize that seeing a picture of her partner on the wall makes her realize "it's not so bad". dido_thank_you_official_video
Following the Eminem sample, "Thank You" reached number three on the Billboard Hot 100 and helped make Dido the world's best-selling female star at the time. The chorus, which thanks someone for "the best