Sometime in the mid-1980s, my stepfather was in need of a 15mm socket. At Sears, he discovered that it would cost about $8 to purchase the specific socket he needed. But a 299-piece socket set cost him about $200. He proudly pointed to the 15mm socket in his new set and told us it had only cost him 67¢. This was my earliest introduction to “spaving”–although no one called it that at the time.

Spaving—a portmanteau of spending and saving—describes the act of spending more money in order to save money. If you’ve ever added an item you didn’t really want to an online order so you could qualify for free shipping, then you have given spaving a try.

Situations like the great socket wrench conundrum of 1986 may seem to clearly exhibit more spending than saving behavior. (Though to be fair, my stepdad still has the “new” set, which was nicer and more durable than his old socket wrench kit.)

But how do you know when spending more to save money is a good idea and when it’s just having you part with more of your money? Here’s what you need to know about making the right spaving decisions for your budget.

Why spaving feels good

There’s a reason my stepdad came home with 298 more parts than he was looking for: It irritated him to spend nearly $10 for a part that probably cost pennies to manufacture. By spending $200 on an entire set—which got him the part he needed for less than 70 cents—he felt like he was getting his money’s worth and being a savvy consumer.

This is exactly what marketers are going for when they set pricing that encourages buying more to save more. Making a purchase already gives our brains a hit of dopamine. But adding a splash of self-congratulation for making a “money-saving” financial decision can short-circuit the part of our brains that reminds us that $200 > $8.

These pricing schemes also trigger your fear of making the wrong financial decision. Online retailers share the exact dollar amount you need to spend to qualify for shipping (or bonus points or a gift-with-purchase) to get you to worry that you’re losing money if you refuse the deal. So you buy something you don’t need to feel like you’re putting one over on the retailer—which, you already know you are not, unfortunately.

Sales events tend to trigger spaving

The insidious nature of spaving is why sales like Black Friday can be such budget killers. You may not have even realized that various sale items existed, but the fact that they are offered at deep discounts tempts you to pull out your wallet. You are being led astray by your brain’s reward center and not giving full thought to whether you need another gaming console.

Even financial experts fall victim to this. Just this week, I was distracted from an Amazon search for shampoo by the Prime Day deals on new Kindle readers. My old device no longer holds a charge, and Amazon helpfully let me know I could get an additional 20% off plus a $5 gift card, on top of the discounted prices for new Kindles, if I returned my old one. Even though I much prefer to read physical books, I took the deal and patted myself on the back for saving 60 bucks. By spending $110.

When does spaving make sense?

Though spaving is usually just a marketing trick, there are times when you actually can use this strategy to your advantage. Specifically, if you are already planning to make a purchase that aligns with a deal.

For example, both my kids needed new shoes, so we went shoe shopping at a store offering a buy-one-get-one-half-off deal. Both kids got the new kicks they needed, and I saved money on the transaction. But if only one of my kids had outgrown his shoes, it would have been better to ignore the BOGO deal because we may have gotten carried away with the idea of saving money and bought a second pair of shoes we didn’t need.

If you already have the intention of buying the number of items (or spending the amount of money) to get the deal, then spaving really can help your bottom line. But if it didn’t occur to you to add the extra items to your cart until you realized that buying more meant saving more, then back away slowly from the deal. You want to be making these decisions, not the marketers.

Spending and saving should be distinct categories

The human brain is easily distracted by dopamine, self-congratulation, and the fear of missing a deal—not to mention shiny new sockets. Which is why it’s smart to decouple the idea of spending from saving because we’re just not wired to make the best decisions when we combine them.

To keep more of your money in your wallet, avoid sales events, which can trigger spaving behavior, and commit to only taking advantage of deals if they coincide with purchases you already planned.

Coincidentally, this is also the best way to avoid being teased about 15mm sockets for 40 years.