The single biggest way shoppers are manipulated by retailers

It's Black Friday, the day after Thanksgiving when Americans take a brief respite from stuffing their faces with turkey to stampede into stores in an effort to take advantage of what appear to be great deals.

But it's a mistake for shoppers to think they're somehow winning at the cost of the retailer.

Sure, it makes sense to buy a good when the price is discounted. But that feeling of confidence is exactly what the retailer wants as they bombard us with not-so-good deals.

Last year, brand guru Martin Lindstrom explained to Bloomberg's Joe Weisenthal that this psychology is the biggest way we're being manipulated by the retailers.

"We fundamentally think we are rational," Lindstrom said. "But the reality is when we are out shopping, around 85% of what we do is irrational. It's subconscious."

That discounted flat panel TV you're about to buy needs HDMI cables and hardwood TV stand, all of which come with fat profit margins for the seller. Those long checkout lines are easy ways for retailers to sell you some batteries or a $2 bottle of water.

"When you go into a store, you are going into the soul of seduction," Lindstrom said. "And the more rational people think they are, the more vulnerable they become."

Keep in mind why we call it "Black" Friday. Back in the day, businesses used ink and paper to keep track of their profits and losses. Red ink meant losses. Black ink meant profits.

Black Friday is when retailers' red ink turns black.