Theres a good chance that youve made a few regrettable purchases in your life. And youre definitely not alone. We all know someone who has given in to an impulse buy or premium price tag at some point. (Guilty.)

But why do we let our spending get out of control, even when we know better? Sometimes our own minds get the best of us. Here are five psychological principles that could be behind your bad spending decisions.

1. Delayed Reward Discounting

Have you ever been so hungry that you decided to hit the drive-through and eat something crappy, even though you could have waited to cook a delicious, healthy meal at home? Or maybe you chose to enjoy one more glass of wine even though youd probably have a hangover the next day?

According to psychologist Carla Marie Manly in Santa Rosa, California, the technical term for this type of thought process is delayed reward discounting. Its the preference for smaller, more immediate rewards as opposed to larger, yet delayed rewards.

Delayed reward discounting is one reason why some people tend to overspend. Better impulse control the willingness to delay gratification is a key difference between those who do not overspend and those who do, said Manly. People who are willing to pause and consider the risks versus the rewards of a spending decision tend to have better spending habits.

Those who are impulsive and do not pause to wait for rewards in the future which may be obtained without such penalties as an overdrawn account or credit card interest get drawn into an unfortunate and costly cycle of overspending, she explained.

2. The Scarcity Principle

The scarcity principle is an economic theory that examines the relationship between supply and demand. When applied to the field of psychology, the scarcity principle basically states that the less available something is, the more desired it becomes. So when it comes to making spending decisions, you might feel more pressure to buy something because you think it could become unavailable soon, according to Vassilis Dalakas , a professor of marketing at California State University San Marcos who specializes in consumer psychology.

For instance, when shopping online, you might see a message like limited-time offer or only two left at this price. Those claims may or may not be true, but, either way, you feel a sense of urgency to buy.

A consumer who was debating whether or not to buy that product is more likely to go ahead with the purchase out of fear that it will go away and he or she will miss out, Dalakas explained.

3. Sunk Cost Fallacy

In economics, a sunk cost is any past expense that has already been incurred and cant be recovered. In the case of a business, for example, sunk costs might include machinery or equipment that was purchased. Since that money has been spent, it isnt factored into future decisions regarding spending.

But sunk costs also come up in our daily lives. And, unfortunately, we sometimes make poor spending decisions based on money, time or effort spent in the past. Thats known as the sunk cost fallacy.

One common example is a gym membership. Maybe you signed up a few months ago and had to pay a hefty initiation fee. However, you dont really love going to the gym after all and rarely make it. Even so, you keep paying your monthly dues because you dont want to waste the money you already spent to get the membership.

The truth is that you arent getting that money back regardless of whether you keep going to the gym or not. So why not save yourself the future cost of membership dues and just cancel?

And buying something you dont need just because you spent a whole day at the mall doesnt make sense, either. Quit while youre ahead.

4. Anchoring

Another psychological principle that causes people to overspend is known as anchoring, which involves how people evaluate price points when making decisions about purchases, according to Dalakas.

For example, say youre shopping for an item with a purchase price of $100. However, that item was marked on sale for $50. Its likely that youll focus on the initial price of $100 (the anchor) and therefore consider the new price of $50 a great deal even if it isnt. The original price might have been inflated, or you might not really need to spend the money in the first place. By concentrating on the anchor, we are actually thinking more about the $50 we are saving than the $50 we are spending, Dalakas said.

5. Social Facilitation

Sometimes, being around other people can help you make better decisions. This is known as social facilitation , or when the presence of other people pushes you to achieve better results. For example, you might run faster if youre racing against other runners instead of a clock, or work more productively in an office environment than at home.

But in terms of your spending, social facilitation might actually work against you. Auctions are a perfect example of how being around other people can encourage you to spend more than you would if you were alone. The idea that others are all vying for the same item creates psychological arousal and makes rational decision-making much tougher. But you dont have to be in the throes of auction fever for social facilitation to take hold; simply spending money with other people around can cause you to make irrational decisions.

So the next time you find yourself in the middle of a bidding war or a friends shopping spree, take a moment to breathe, let your heart rate slow and reconsider whether youre really willing to spend that much.