For me it's when I can't see anymore growth for a particular household after playing it for over 6 to 8 years. And then I get inspired for a next story. In fact, I just did that with my newest household. I brought back Cleopatra Selene who was the daughter of Queen Cleopatra of Egypt. I deleted her whole family & aged her up to a young adult. I gave her the necessary traits, personality likes & dislikes. Then I made her husband, King Juba of Africa. (I had to google that info). Anyways their love story that I created is that her loving husband wanted to combine his Culture with hers because she's lost so much & wants to please her.
