Borrowing the scaling theory of Anderson localization in condensed matter physics, I argue that tunneling from a large cosmological constant site in the stringy cosmic landscape is fast, while tunneling from a small cosmological constant site may take exponentially long time. The critical cosmological constant value is estimated to be exponentially small compared to the Planck (or string) scale. This suggests why our universe has such a small cosmological constant. It also suggests an inflationary scenario with repeated fast tunneling.