Overnight success is pretty rare. No matter what line of work–business, entertainment, politics, etc.–almost every example of someone who's been very successful is a story of years of hard work that eventually paid off.
The same can be said of overnight failures. They almost never happen. Unless someone makes a catastrophically bad decision or takes a risky gamble and bets it all, it takes time to officially become a failure.
It's easy to assign a lifetime of importance to one grade, SAT score, or admissions decision from a college. But there is no overnight success or failure at 17 or 18. If something goes well, celebrate it. Duplicate the effort and go after more wins. If something goes badly, learn from what went wrong and do it differently next time.
But whatever you do, remember that consistent effort is a lot more important than any one result. And that's never more true than when an admissions decision arrives.