None of you'se guys mentioned Airworthiness Directives that pop up from time to time, Service Bulletins, insurance deductables when it gets wrecked, time not producing income because it was wrecked, money to pay lawyers to sue the guy from Angola who won't pay you even if you do get a verdict in your favor, the airplane that won't start at an airport that has an FBO that will "help you out" for $1200.
Two decades of aircraft ownership, and only a tiny bit of that with leasebacks/rentals.
The best way to make a small fortune in this endeavor is to start with a big one.