If you don't track your personal spending, start now. Your life is a little business. If you save 25x your annual spending and invest it properly, you can declare financial independence, withdraw 4% a year, and live off your investments FOREVER.

I used to run Profit & Loss (P&L) statements for projects at a corporation and first learned the basics that way, but the paragraph above is what really opened my eyes. Once you have skin in the game the numbers become far more meaningful.