100% correct, sir! I'm not the sharpest tool in the shed when it comes to money - but was taught this a long time ago. To get rich (relatively speaking) cheap money is your friend.

Got a mortgage at 2.5%? Awesome! If you have extra to pay off early, put it in an index fund instead. Not only is that 2.5% cheap money - you even get to deduct the interest on your taxes. (That's a whole other kettle of fish though - how come this deduction is considered a "right" by rich folks, while anything done to help those in the bottom 80% is a handout??)