Yes, Joshua was the nation's military leader and knew the burden of leading. Yet, he had always had Moses to encourage and remind him. As I see it, it is very likely that Moses spent much of his time mentoring Joshua to remember all that God had done to protect and provide for His people. Joshua was one of only two men that were delivered out of slavery in Egypt and also crossing the Jordan River into the Promised Land. All other adults had died while the nation wandered in the desert. It was vitally important that Joshua remember God's faithfulness as he lead the nation after Moses's death.
In Joshua, chapter 1, we see God's encouragement to Joshua as he becomes the leader of Israel. Three times, God instructs Joshua to "be strong and courageous." He also reminds Joshua that, as Israel's leader, he must obey all of God's commands. Obedience would ensure the nation prosperity and success. This obedience is not out of self-will or legalistic discipline. Rather, it is an act of love and honor for all that God had done and would do for His people. Obedience sourced out of a deep and genuine love.
At the end of chapter 1, we see the response of the nation to Joshua's appointment as their leader. First, they tell Joshua to "be strong and courageous." This is the fourth reminder to Joshua. I think God really wanted him to hear this. As the successor to Moses, he was probably, and understandably, fearful and doubting himself. How could he ever live up to the standard Moses had set. The key is, God did not want Joshua to be Moses. God wanted Joshua to be Joshua... strong and courageous! So, the people remind Joshua of God's instruction and while providing their vote of confidence.
Joshua 1:17-18 - Just as we fully obeyed Moses, so we will obey you. Only may the Lord your God be with you as he was with Moses. Whoever rebels against your word and does not obey your words, whatever you may command them, will be put to death. Only be strong and courageous! (NIV)
This was his nation to lead. He was committed to God and knew God would do what He had promised. Joshua looked to God, not at the circumstances. Joshua believed God.
Do you?