Naive set theory says that for every property, there's a set of things that have that property. Bertrand Russell asked, "what about the property of being a set that's not a member of itself?"
This is, traditionally, seen as a bit of a problem for naive set theory.
Classical theism says that an entity exists who can perform any action. Many people have asked, "what about the action of creating a stone so heavy that he himself can't lift it?"
This sort of thing used to be a bit of a problem for classical theism.
That was before Rick Warren solved all of these problems forever.
Check it out.