Joshua revisited
Like Moses, Joshua was born in Egypt. He would have experienced the same trials as the rest of the Hebrews and seen the same miracles prior to the Exodus.  Joshua assisted Moses from his youth. I think that both observation and participation prepared him during the years of learning for the years of leading.  But think about this:  Joshua began assisting Moses when a youth (before reaching the age of a man?) and served in that capacity until Moses died.  What a long internship that was!  We have nothing in Scripture indicating that Joshua was ever impatient with his position as number 2, only indications of his diligent service.
As I have reflected on Joshua--as well as Joseph and Daniel--I can only conclude that Joshua saw his service not only to Moses but as unto God, and a personal God who Joshua knew as faithful and powerful.
And  when God put Joshua into the leadership position for which He had groomed him, Joshua was never one to dawdle.  Whenever God revealed His will to Joshua, Joshua acted immediately.  I'm not saying Joshua was a perfect leader; we saw that in chapter 9 when the Gibeonites deceived him; but he was a man of God who sought to do God's will with a whole heart.  And he told God's words without changing them to suit his audience either.  Joshua was uncompromising, trusting in God's promising.  What an example to us all!