When it comes to Compound interest, I always think of Einstein who said:

"Compound interest is the eighth wonder of the world. He who understands it, earns it … he who doesn't … pays it.”

I couldn't agree more and it's why people should pay off bits of their mortgage above and beyond normal repayments if they can afford it. The sooner you can get to a point where your principle repayment is higher than interest the better