It's polite to give notice when you move out.
Madeline is Cynthia's only tenant, and Cynthia relies on Madeline's rent money to pay her bills.
Madeline wants to move out of Cynthia's apartment.
Madeline gives Cynthia a two-month notice before moving out of her apartment.
Having already paid this month's rent, Madeline packs her things and moves without saying goodbye or giving warning to Cynthia.
Cynthia is able to line up a new tenant who will move in once Madeline is gone, assuring that all of her bills continue to be paid on time.
Expecting Madeline's rent money to pay next month's bills, Cynthia ends up late on many of them and struggles to catch up for a while.