1. Married a frugal woman. Not sure it's a sacrifice, but it's the biggest factor!
2. Started a business from scratch. For several years, every single night and weekend was spent working the business in addition to my regular long-hour, high-stress job. Huge sacrifice of time.
3. Followed Dave Ramsey's money advice. Paid off credit cards, only took modest vacations, paid cash for used cars, budgeted like crazy, which eventually led to ...
4. Paid off our mortgage!
Now that we have no bills, a strong income and crazy-good budget discipline, paying for flight training is a piece of cake. We'll have no trouble buying and operating a plane now, but it took years and years of sacrifice to get to this point.