visitors to stay for a limited time.
However, when the time comes for us to leave, our Host has enjoyed Himself so much that He asks us to stay another day.
A different explanation is that Sukkot is a holiday intended for all of mankind, but when Sukkot is over, the Creator invites the Jewish people to stay for an extra day, for a more intimate celebration.
Shemini Atzeret also marks the beginning of the rainy season following the harvest in Israel.
The only ritual that is unique to Shemini Atzeret is the prayer for rain, Tefilat Geshem.