[tw1010]

Polya's text was targeted towards researchers and people who already understood the basics pretty well. But I don't think the analogy approach is valid (or at least, not recommended) in the context of this thread, where the parent seemed to assume that the audience wasn't even particularly comfortable with limits. It can be a dangerous and seductively-easy path to go down, is all I'm saying. You're not going to understand mathematics without having a firm firm grasp of the rigorous definitions and by doing mountains of exercises (where it will often be quickly apparent that using an analogy is not sufficient).