3 Reasons Why:
1: You start within the only crystal in the game, and if you press any directional key at any time, you win! It's that simple! So technically the only way you can 'lose' this game is by quitting.
2: The map is a perfect square, so you can't exploit any glitches that allow you to leave the provided playing area, and even if it wasn't, reason #1 wouldn't allow you to reach the edge of that playing field.
3: Because I said so! (LOL!)