I think it really depends on the individual. If you're a fool with your money, you're destined for failure in any venture. On the other hand, if you're a hard worker with a good head on your shoulders, you can make a living buying and reselling storage units. Are you going to get rich doing it? Probably not. But to me, the excitement and freedom we enjoy in this business is priceless.
I have to agree with you there. Don't be a fool with your money. I was, and it put me out of business. You can be successful for awhile, then make one stupid decision and ruin yourself. This applies to any business.
Also, like Cobia said, start with a lot of money. Like any business, you want to keep your overhead low, and focus on sales. There's a saying, you make money when you buy, which is true in the sense that you need to get the best deal possible to turn a profit. However, you truly only make money when you sell. If you can't sell your items, and you keep buying, eventually you'll be overwhelmed to a point where most people give up. If you really want to do this for a living, you need to be great at every end of the spectrum, or find a partner who can excel where you fall short.
But like Travis said, the business is probably the most exciting and rewarding thing I did in my life. The "rush" of going through a storage unit never goes away. Every time you buy one it's the same feeling you got about opening Christmas presents as a child. It's probably the closest thing to that feeling I have gotten as an adult. But then, it's time to get to work - not play.