What was the reason for athenians' defeat in the pelonnesian war

The Peloponnesian War was a war between the Greek city-states of Athens and Sparta.  This war lasted 27 years from 431 B.C to 404 B.C. and ended with a Spartan victory. In general, Sparta had a powerful army and was able to control land battles and Athens had a powerful navy and was able to control the sea.  Sparta was able to eventually win this war for several reasons.