Original Sin

Did you ever read a more cogent, succinct defense of the obviousness of the truth of the doctrine of original sin?
As PapaRatz says, we can see the proof of original sin's existence all around us, in us.
"In effect, there is a contradiction in our being. On the one hand we know we must do good, and in our inner selves this is what we desire, yet at the same time we feel an impulse to do the opposite, to follow the path of egoism, of violence, ... though we know that this means working against good, against God and against our fellow man. This inner contradiction of our being is not a theory. We all experience it every day."
Don't we? Doesn't this contradiction in our very selves, these conflicting impulses in virtually every situation in which we find ourselves called to make a decision, inform our entire lives?
Or am I the only one who needs to fight the fact that I can always think of a good reason to do a bad thing?

(And I'm left wondering, as so often, how does that little old college prof manage to say things that I, with my impatient third-grader's approach to things, can actually grasp?)