What are some good topics for a monologue?

A monologue is when an actor talks for awhile, either to himself, to the audience, or to someone unseen. In "Fiddler on the Roof", Tevye has a monologue where he talks to God about why he couldn't have had just a little bit of a better life. You can find monologues online that don't have anything to do with plays, too."To be or not to be" in Hamlet is another example in literature as well as the poem "The Raven" by Edgar Allen Poe.