A couple of days ago I walked into a bike shop to buy an inner tube. It cost five dollars. As I opened my wallet, the guy at the register reached for the credit and debit card processor. “Oh, you’re paying cash?” he asked. “It’s funny. Hardly anybody pays cash anymore.”

His tone was almost wistful, as if he were one of the last merchants to accept an ancient Roman coin. We started talking. We agreed that cash might soon be obsolete. Paying with a card is so much more convenient.

Credit cards also offer perks. Plenty of travel hackers write about getting free flights, flight upgrades and free accommodation based on credit card air mile rewards. To stockpile points, they try to use credit cards to pay for every purchase. They’re also careful about the cards they select. Chase Sapphire Preferred and American Express are among travel hacker favorites.

But only those with ironclad discipline are likely to come out ahead. Like a carnival gamer that wins a giant stuffed toy, most don’t realize they’ve paid enough to buy two fluffy prizes.

After all, when we open our wallets and remove cash bills, we’re more aware of what we’re doing. We see cash physically changing hands. With a credit card, it’s different. Somehow, it’s a lot less real.

As a freelance writer, I travel full-time. Over the past 12 months, my wife and I went through Europe on a tandem bike. We visited much of the Middle East. We also checked out Ethiopia, Kenya, Tanzania and Thailand. We’re like plenty of other bargain travel junkies. But we don’t rabidly pursue credit card air miles points.

That doesn’t mean we don’t use credit cards. We do. We also collect air miles points. But we don’t charge every purchase. Some travel hackers might laugh. They might call us rookies. But in most cases, it’s the guy at the carnival that has the final laugh.

Many travel hackers lose more than they gain. Whether you travel, or stay at home, paying cash instead of credit can save a lot of money.

In 2001, researchers Drazen Prelec and Duncan Simester published, “Always Leave Home Without It: A Further Investigation of the Credit-Card Effect on Willingness to Pay.” Their studies refer to what they call, “the credit card premium.” They found that the willingness to pay for something with credit, as opposed to cash, increases the amount that people are willing to spend by 50 to 200 percent.

In one study, they offered tickets to a Boston Celtics game. The hometown team (Boston) needed the win to take the division title. The subjects were MBA students at the Massachusetts Institute of Technology (MIT). Researchers wanted to know how much the students would pay for the tickets. They were split into two groups: one that had to pay cash and the other that had to pay with a credit card. On average, the students who had to pay cash offered $28. The students who had to pay with a credit card offered $60.

Expenses feel real when we pay with cash. That’s why the credit card group bid more than twice as much. This phenomenon hasn’t escaped organizations that charge highway tolls. In a paper published in The National Bureau of Economic Research, Amy Finkelstein reported how highway gatekeepers can get away with charging more. Many highway tolls still require cash payments. But once they convert to an electronic payment system, they jack the price 20 to 40 percent. Few people recognize how much more they’re paying.

In 2014, Business Insider reported a study conducted by Dun & Bradstreet. They found that people spend 12 to 18 percent more when they use credit cards instead of cash.

McDonald’s also reported that the average customer pays 55 percent more when they pay with a credit card. The average bill is $7 when people use credit cards. It’s $4.50 when they use cash. Of course, people might feel silly pulling out their Visa to pay for an ice cream cone. But something similar happens at higher-end restaurants.

In her book, Mind Over Money, Claudia Hammond references a study at a restaurant in West Lafayette, Indiana. The restaurant recorded customers’ tips as a percentage of each bill. They found that people paid higher tips with credit cards than they did when they paid cash.

In 2011, Manoj Thomas, Kalpesh Kaushik Desai and Satheeshkumar Seenivasan published, “How Credit Card Payments Increase Unhealthy Food Purchases” in the Journal of Consumer Research. They examined the shopping behavior of 1000 households over a six-month period. When customers paid with credit or debit cards, they bought more unhealthy food.

They might have also paid lower overall grocery bills when they paid with cash. In a second experiment, the researchers tested to see if subjects bought higher quantities of healthy food based on their method of payment. Healthy purchases remained the same, regardless of the payment method. But once again, the subjects added more unhealthy products when they paid with a credit or a debit card.

Some people might be able to charge almost everything to their credit cards. Some might be disciplined enough to clear the balance every month and avoid interest payments. Some might never fall for extra impulse buys. Some might shop for deals. They might treat credit just like cash. They might stockpile points for a free flight once a year. But, like that bunny winning guy at the carnival, most of them pay much more than they might think.

Andrew Hallam is a Digital Nomad. He’s the author of the bestseller, Millionaire Teacher and The Global Expatriate's Guide to Investing: From Millionaire Teacher to Millionaire Expat.