One can do this even when they are absolutely 100% positive that they are correct. The lesson is in the experience of actually doing it.
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I'm not much for the "dualism" deal. Can't have valid if there is no invalid, or can't have joy without knowing pain, etc. Nope. Yin Yang. Big, small, fast, slow, tall, short, right and wrong. Nope. Our universe has far more dimensions than just the two. This or that? I'll take the other thing anyday.