What’s something about math that still amazes you, even after knowing it for a long time?

My answer to a Quora question: What’s something about math that still amazes you, even after knowing it for a long time?

That mathematics is consistent: regardless of how long and complicated are proofs, everything miraculously gets worked out without contradiction.

Mathematics is an ideal world; what strikes is its stability. You may revisit some its corner after being away for 30 years, and discover that everything there is the same as it was when you left it.