I've heard compactness described as one such concept. https://math.stackexchange.com/questions/485822/why-is-compactness-so-important https://math.stackexchang

I've heard compactness described as one such concept. https://math.stackexchange.com/questions/485822/why-is-compactness-so-important https://math.stackexchange.com/questions/485822/why-is-compa...