The band revealed that the song was written about a young girl from Kitchener with a canceroustumor in her brain named Mina Kim. The "thief" mentioned in the song refers to the tumor. The short clip at the end of the song consisting of a young girl singing a Sunday school song is a real audio clip of Mina Kim singing "Little By Little" with Maida's wife Chantal Kreviazuk and band member Jeremy Taggart.
The Micha Dahan-directed music video of Thief was filmed on May 2, 2000 on a rooftop in downtown Toronto and premiered on Muchmusic on May 23. It was shot entirely under a rainy setting on an otherwise sunny day, to impose the mood given by the song. Band members do not play instruments and are shown in slow motion film stock in the rain.