"Good luck!" makes me feel like it leans pessimistic. Instead of saying something positively assertive, as in you don't need luck. "Good luck!" is a pessimistic phrase. It encourages, as the psychologists say, an external locus of control. In non-psychology-speak, this means the phrase "good luck" encourages us to see events as outside of our control (as opposed to within our control). When we perceive outcomes as outside our control, we don't work to affect them, leaving us in the passenger seat of our lives. "Good luck!" implies, to the person you're saying it to, that they need luck to succeed. Instead of encouraging or helping them, you're wishing for the world to conspire in their favor. If you had a friend who was about to compete in a contest, you wouldn't tell them: "I hope the judge is feeling lenient today" but to say "Good luck!" is to say the same thing. "Good luck!" is a terrible phrase no matter what your religious orientation. If you are a theist, and believe in God, it's bordering on blasphemous. Why are you appealing to a nonexistent "luck" when it is God who directs the events of the world? If you are an atheist, it's a meaningless statement because it acknowledges there is no way for you to affect this luck. Either way, you're out of luck. So, we should say: You'll do great: Instead of merely wishing positive things, this communicates confidence in who you're talking to. I believe in you: While "You'll do great" communicates confidence and assurance, "I believe in you" communicates personal faith. Knowing that someone else personally believes in you is an incredibly reassuring feeling. Best wishes: If you're looking for something formal to go in an email, this is a good alternative. "Best wishes" is polite and appropriately formal for email sign-offs or meetings. Fingers crossed: This is more of a casual alternative to "Best wishes" Hope it goes well: If you want to stick with the traditional meaning of "I want the best", you can stick with saying "Hope (whatever it is) goes well" and also say "Wish you well"
