Babi - if you're teaching history and you are a GOOD teacher you are never teaching the same things over and over. Each class takes the discussion in a different direction, if the teacher lets them. I kept reading new articles and books, giving me new information, both because there was new research and because it was just something i hadn't read about before.
Now, if you're teaching math, maybe 2+2 is always 4, but just think of all the new biographies that have come out over the last 50 yrs. Just watching Ken Burns tv programs on the Civ War, or the Brooklyn Bridge, etc. or the John Adams' series, including Abigail, and all those other Founding Fathers and Mothers, or books on WWII, or the Viet Nam War, or the Civil Rts Movement, or ALL the books on Lincoln, including Mary, and ALL the books on women's history over the last 50 yrs., etc. etc. Each gave me new info to relay or to bring to an event or person. Actually, that's a big part of what i liked about teaching history..............jean