The biggest threat to your finances could be your friends.

It may seem counter intuitive that the people closest to you could negatively impact your financial life, but too often, people will spend more than they can afford in order to keep up with the lifestyles of those around them.

It’s called “relative deprivation,” and it’s basically the scientific term for “keeping up with Joneses.”

The idea is this: You can be perfectly happy with what you have, but as soon as you look around and see that others in your inner circle have more, you become unhappy with what you have, feel suddenly deprived and desire more.

Relative deprivation is hardwired into us. Researchers Sarah Brosnan and Frans B. M. de Waal tested this theory on some Capuchin monkeys (and it’s been reproduced with dogs, birds and other monkeys since).

They took two monkeys and put them in a crate next to each other. The monkeys, who could see each other through a clear partition, would hand the researchers a rock in exchange for food. At first, they both got cucumbers and they were perfectly happy doing the exchange 25 times in a row. Then, the researchers changed the experiment. The first monkey completed the task and got a cucumber. The second monkey did the same, but he got a grapes.

Monkeys like cucumbers, but they absolutely love grapes, and this created a problem.

The first monkey quickly caught on to the inequity. He was working just as hard but getting a lot less than his buddy. When he handed the rock over again and was again offered a cucumber, he hurled the cucumber right back at the researcher and threw a fit. While the cucumber was fine at first, it became a completely unacceptable reward once he saw his friend was getting grapes.

We do this all the time. We’re constantly comparing ourselves to those in our immediate circle and looking for areas where we’re not getting what we think we deserve, financial and investment advisor Robert Pagliarini recently wrote at Daily Finance.

He calls it the financial creep, where, in an attempt to keep up with those around you, you ignore what’s best for you. It’s the same reason we can spend hours reading financial advice on blogs like this one and not implement it—because at the end of the day, your work friends eat out every day for lunch or your Facebook friends are taking tropical vacations and you want to do the same. Suddenly, your brown bag lunch or staycation isn’t as exciting.

Eventually this creep leaves you living a lifestyle you really can’t afford. And the reality is, you would be just as happy living a simpler, more modest life if you weren’t constantly comparing.

So next time you see your friends enjoying something and you want it, ask yourself: Is this really something I want? How much value will it really add to my life? Would I be just as happy without it?

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