As wiser, deader Yoda explained to Luke in TLJ, failure can be a great teacher. Trying and failing can be a great learning experience. Doubts are human. You know who doesn't experience doubt? Psychopaths. This is one of those pieces of advice that sound super wise, but are, in fact, utterly useless and potentially harmful. These films are iconic, and Yoda is posited as the ultimate teacher. And him giving this advice to Luke is both harmful to Luke (who would later take a big failure so hard he exiled himself for YEARS), and, more importantly, to impressionable young minds. Failure is how we learn. And learning to move on from failure is an important lesson.