There are people all around who are constantly making bad financial decisions in their lives. Some of these decisions are just really bad and benefit nobody. Some bad decisions may benefit one other individual or a small group of a individuals. Someone with a major gambling problem loses a lot of money and the casino owners benefit.
But there are also some widespread financial errors in which you can benefit in your everyday life. You should thank these other individuals for their bad decisions that enable you to gain an edge. Of course, I would just say "thank you" inside of your head and not literally to their face.
You can thank all of the people out there who don't pay off their credit card balance each month (with the exception of those who have 0% interest). This allows credit card companies to offer bigger rewards, including cash back. So you can use your credit card, delay the payment coming out of your checking account, pay off the balance each month so that you don't pay any interest, and, in most cases, you are still just as eligible as anyone to get cash back or other rewards for your purchases. If we didn't have all of these people with high credit card debt paying high interest, then this would not be possible.
You can thank all of the people who do regular food shopping at drug stores and convenience stores, where the prices are usually marked up significantly. It makes little financial sense to do your regular shopping in these places in most cases. It is far cheaper at a grocery store, or even more so at Target or Walmart. But if I ever have an emergency where I need some milk or butter, then I can run into a gas station convenience store, maybe even on a major holiday, and get what I need. I would never do any large purchases at one of these convenience stores unless it was an emergency. But in this case, they really can be "convenience stores". I'm not sure if they could stay in business though if it weren't for their "regulars".
You can thank all of the people who make monthly payments on their car insurance and homeowners insurance when they have the option of paying it in full upfront and getting a significant discount. You can often save hundreds of dollars over a 6-month period over over an annual period, just by paying it in full at the beginning. This is huge savings, especially when you can't even get a 1% interest rate on your savings in a bank. If it weren't for all of those people making monthly payments (probably because they live paycheck to paycheck), then these significant discounts would probably not be available.
On a bigger scale, you can thank the Chinese government and all of the Chinese workers who export inexpensive products to the U.S. If the Chinese would simply let their currency strengthen and not be obsessed with exporting, then the Chinese people could consume much of what they produce. Instead, they prefer to subsidize American consumers, while buying overpriced U.S. government debt. I'll take the subsidy while it lasts.
What other things can you think of where you can benefit at the expense of others because of their poor financial decision making? They are often all around us, yet we never stop to think of them.