Good luck!の意味です。でも舞台関係者の間で、Good luck!というと逆に縁起が悪いことが起こるという迷信があり、逆手をとってBreak a leg!（脚を折れ！）というようになったそうです。
Steve Jobs - from a speech at Stanford univ. -
You can't connect the dots looking foward. You can only connect them looking backwards. So you have to trust that the dots will somehow connect in your future. You have to trust in something- your gut, destiny, life, karma, whatever. Because believing the dots will connect down the road, it gives you confidence to follow your heart, even it leads you off the well-worn path. And that will make all the difference.