Tumbling dice are governed by the laws of physics, which are deterministic. The outcome is predetermined by the motion of the atoms within the dice and the air, and whether you win or lose cannot be altered, before the dice even hit the table.
When you blow on the dice, the breath comes of your own will, from the action of your mind and soul, which physics cannot explain and is non-deterministic. By blowing, you are introducing true randomness into the motion of the atoms (not the fake pseudo-randomness of stochastic mechanics!). This is the only time that luck can come into play. If your soul has strong aura, then you can use your breath to imbibe the dice with good luck and win for sure.