People often consider success and failure to be antonyms. But, are they? If you never experiment, how can you expect to make progress? And if experiments never fail, then it begs the question whether they're testing hypotheses that could ever lead to meaningful progress. No one is successful simply by trying something once. So, if you believe that progress is part of what makes a person, project, or product successful, then it's important to acknowledge that failure is a vital ingredient, not an inhibitor.
By always doing things that you know you can comfortably accomplish, you can guarantee that you'll never fail. But, that's just settling for mediocrity. Success requires taking risks, and with every risk comes the possibility of failure; it's part of the process. Instead of being scared of the consequences of failure, fear being satisfied with mediocrity.