By microscopically observing widely used data files, we identified the considerable room for life time improvement in NAND flash memory, which is due to the discovery of a non-uniformity in bit-level data patterns. In an attempt to exploit the discovery, we propose a novel bit-level wear-leveling scheme. Instead of considering only the view of page-level or block-level, we incorporate the non-uniformity in data encoding patterns into wear-leveling scheme. Because of its orthogonality to the existing block-level wear-leveling approaches, our solution can be adopted over the existing solutions without considerable overhead and extend NAND flash's life span up to 36% in case of SLC.