When Paris of Troy abducted Helen (or did they elope? depends on who you believe), her husband Menelaus demanded of his brother Agamemnon, king of the Greeks, and all the other Greeks, help in retrieving her. Agamemnon agreed because if he had not done so then no Greek woman would have been secure since the other nations would have seen the Greeks to be passive in the face of an abduction.
So Agamemnon assembled a huge army ready to sail over to Asia Minor (present-day Turkey) for the siege of Troy and in order to bring Helen back to her husband. This was in a time before the Greeks had standing armies, and so each Greek left behind his trade and farmlands to go on this mission from which he might never return, and thus made a considerable sacrifice.
However, the fleet was becalmed. No wind blew. This went on for some time, until the army grew restless and began to suspect there was something inauspicious in it all. Agamemnon was forced to consult the oracle to find out if divine displeasure was the cause. The reply came that although all the Greeks had made considerable sacrifice to go on this expedition, Agamemnon himself had made none.
Now this is the secret of leadership when it is a divine affair. If the leader does not move, does not sacrifice, the entire army is becalmed and nothing can happen.