I've always been reasonably solid in managing my finances. I have a pretty good income now so it's fairly easy, I can max out my 401k contribution, indulge in my hobbies, and still have money left over.
But 7 years or so ago when I was struggling to find good work to make use of my Comp Sci degree, and was working as a video game tester I still managed to save money. When I lost my pretty bad testing job and ended up at bottom of the barrel next to guys right out of high school testing job, I downsized from sharing an apartment to renting a room in a house, and still saved. Not a ton of money, but still.
On the other hand, the people I know who are in debt... their income doesn't matter. When they're not making much money, they spend it all, and then some. If they get a new job that pays more, do they pay off their debt? Nope, they immediately find a way to spend it. Some even pile on more debt. Others just stabilize it, but for reasons I can't figure out people don't pay down their debt when they have the ability to do so. It makes no sense to me.
A friend of a friend is the worst example of this. He doesn't work, he lives off of benefits. But he also lucked out and has some mineral rights in North Dakota or something, which results in him getting a check every month. Now granted, this income would put him off of benefits, but he doesn't report it, pay taxes or anything. So, he's evading taxes and defrauding government assistance programs. Ignoring all that.. the mineral rights check varies based on how much oil they pump out of the ground in a given month. So it is anywhere between $1,500 and $5,000. But, it doesn't matter. No matter the size of the check, he spends every last penny, and is completely out of money before the next check gets there. He has $5,000 dollars this month? Time to buy the gf some jewelry, time to buy a new TV, time to trade up on the car, time to go on a trip!
That's not to say I'm perfect, I have some flaws in how I manage my money. First of all I spend way too much money eating out. I need to come up with a learn-to-cook plan of some sort. It would help from a health standpoint as well. I also do a bad job of investing, the 401k is nice and easy... but aside from that my money is rotting in a very low interest. There's a lot more in there than I need for emergencies, so I really should figure out a way to make the rest of it work for me. Part of it is me being risk-averse, part of it is me thinking it is a soon-to-be down-payment on a house, but the market has rebounded a bit, and even when it was at its bottom I still couldn't quite afford something that I would actually want to own.