His mother’s boast that he would rule the world due to her conniving (she arranges the murder of her husband when he gets a second wife — which threatens Alexander’s chances at the throne). But having the world proves hollow for the successful general. He can trust no one.
It’s lonely at the top.
Friends are better than riches and accomplishments, which all remain here on Earth and convert into dust when our immortal souls pass into eternity. Friendships alone remain.