Forget the first snow, Dec. 1, or the first time Christmas carols start playing in stores – if you work retail, you know that the true start of the holiday season is Black Friday.

And Black Friday is also pretty newsworthy. An increasingly popular "holiday," Black Friday has been the biggest shopping day of the year since 2005. And it also makes headlines for, well, less-than-pleasant reasons.

Take 2018, when the Los Angeles County police had to intervene after angry shoppers got in a fight at a local Walmart. Or 2013, when a 34-year old Walmart employee, Jdimytai Damour, was trampled to death by a mob of shoppers.

So why can Black Friday turn even smart shoppers into spendaholics, and turn retail crowds into angry – and even deadly – mobs? It all comes down to the psychology of spending, and how stores "trick" you into buying more. Here's what happens.

All that media attention in the lead up to Black Friday affects your brain – and makes you want to go shopping, even if you don't have any particular purchase in mind. That's because it seems like everyone is out scoring a great deal, which can trigger FOMO, or the fear of missing out.

As Psychology Today explains, FOMO can capture your brain's attention and make it hard to think about anything else. So you'll naturally become more preoccupied with shopping. Research also shows that social media use can increase FOMO – so seeing your friends' new purchases on Instagram can make you more likely to shop.

Finally, researchers have discovered that most people feel the most FOMO at the end of the day and at the end of the week – so since Black Friday is, obviously, on a Friday, your sense of FOMO might feel especially strong.

The mega-discounts you'll find on Black Friday also make it harder to think twice about your purchases. As neuroscientist Christian Elger explained to DW, words like "sale" and "deal" can trigger the natural reward systems in our brain. And when those reward centers are active, the parts of your brain that would naturally reign in your behavior – and make you think about whether you really need something – become less active.

In other words, your brain starts telling you to spend, spend, spend.

Black Friday also spurs on more spending through scarcity. Black Friday deals typically only last one day, so you can feel like you need to buy everything right now. And since most retailers intentionally limit their stock during Black Friday, shopping can feel especially urgent.

So why does Black Friday turn everyday shoppers into angry mobs? Well, those same parts of your brain that would limit spending – you know, the ones that become less active when you see a sale? They're also responsible for reigning in other aspects of your behavior. Overall, you may feel less inhibited, and more likely to get aggressive when you feel like you have to compete with other customers over limited stock.

As PBS explains, super-early Black Friday sales also contribute to customers' bad behavior. Sleep deprivation can make shoppers more aggressive. Plus, large crowds can naturally make you more anxious and aggressive, so the uber-packed stores you'll see on Black Friday could tempt you to misbehave.

So how do you keep yourself (and your wallet) safe this Black Friday? By understanding, and working against, the psychology of overspending. Try these tips to make smarter choices.

• Window shop in advance. Getting caught up in the rush of Black Friday can mean you'll make purchases you wouldn't have made otherwise. Choose beforehand what you'll buy, and avoid impulse purchases.
• See if the sale is actually good. We'll let you in on a little secret: Many stores raise their prices before Black Friday, so their discounts look like an especially good deal. So pay attention to the price of the item you want – you might find as good a deal in December, and be able to avoid the crowds.
• Be aware of mob mentality. Simply acknowledging that Black Friday can make you more aggressive might be all you need to reign yourself in. And if you know you tend to get anxious in crowds? Try shopping online, the next day, or later during the day, when stores tend to be less packed.