Joshua witnessed Moses lead the Israelites out of captivity, stretch his hand over the sea to part the waters and receive the Ten Commandments.
Then Moses died.
Joshua’s mentor and friend was no longer with him. Joshua could claim that without Moses leading him he could do nothing. He could have said that he wasn’t prepared to be the leader of a nation without Moses to turn to for guidance. 
But he didn’t. Joshua realized that Moses was a blessing from God, not God. He knew that God would be the one to continue to provide for him.
It is good to learn from the people that God places in your life, but remember that God should always be the source of your strength and confidence. 
Joshua 1:1-2