An artist may be able to create without knowing how to teach others how to create. That doesn't make him less of an artist. But even if an artist is not a great teacher, given a pupil of spirit, that pupil will flourish with very little instruction. Yehoshua's was like the Moon. Because he was 'a man of spirit', he shone from the inspiration of his teacher Moshe.
A look in this week's Torah reading Pinchas to understand why Jewish women usually get it right with regards to bringing Redemption...and why Jewish men so often don't.