Around the world, there are 94 million people who have a Costco membership card. Celebrities have them: Chrissy Metz of NBC's "This Is Us" is an executive member "because we buy a lot of toilet paper," she says. There are Instagram accounts devoted to Costco, such as @costcodeals, and websites, such as CostcoInsider.com. Costco has even become a travel destination — one fan says she has been to 70 Costco stores during her travels. And at least one couple got married at Costco. This level of enthusiasm for a grocery store may seem odd to some — unless you're a Costco shopper.

Chrissy Metz of NBC's "This Is Us" shows off her Costco membership card CNBC

"Some of their customer base is absolutely addicted to Costco — absolutely addicted to the experience and the brands and the thrill of going to Costco," Patricia Hong, partner at the global management consulting firm A.T. Kearney, tells CNBC Make It. And that is by design — inspiring obsession is all part of Costco's playbook. Costco gets you hooked with everything from psychological tricks to the layout of the store and its extreme value.

Membership feels exclusive

To shop at Costco's warehouse-like stores — which sell everything from food and toiletries in bulk to clothes, electronics and diamond rings — you have to buy an annual membership for either $60 (household or business) or $120 (executive). That makes the store feel "a little exclusive" and thereby more appealing, says Paco Underhill, author of "Why We Buy: The Science of Shopping." You have to be a part of the "club" to even enter. But more than that, there's a psychological aspect: Since membership fees are a "sunk cost," consumers try to justify it mentally, which results in them shopping more frequently and buying more products each trip, according to Kusum Ailawadi, author of a 2017 study on club shopping. "You'll say ... I'm going to make sure I get my money's worth by shopping in the club store every chance I get," Ailawadi told KTLA. As Underhill says, the membership card "vibrates" (metaphorically) in your wallet. "I have spoken to people that go and drop into a Costco three, four times a week," Hong tells CNBC Make It. Of course, not everyone believes the membership fee is exclusive, or even worth it, and it may not be if you don't shop at Costco regularly, if you live alone, have little space to store bulk-sized items or are unable to resist impulse buys. Still, the company says it has a 90% renewal rate in the U.S. and Canada and 51.6 million paying memberships (each of which can have multiple cardholders). "They have a very loyal membership base," Hong says.

Everybody loves a deal

Consumers go crazy for a deal, and Costco has designed its entire strategy around this core tenet — even if it means resisting the urge to raise prices and increase profits. A good deal "feels like winning," says Bob Nelson, the senior vice president of financial planning and investor relations at Costco. "Would you rather win or lose?" Value is the driving force behind Costco's sales strategy, according to Nelson: "The definition of value for us is highest quality, lowest price and best member service." Part of that equation is that Costco is "an item business," according to Nelson. Every item on its warehouse shelves is meant to be the best in its category. That means there are only between 3,700 and 3,800 items for sale per warehouse, Nelson says. By comparison, a Walmart supercenter sells 142,000 different items, according to Walmart's website.

Shopping at Costco is a journey

Going to Costco is more than just a grocery run; the map for shopping there is strategic to draw customers in, keep them there and ultimately make more sales. It all begins with the store layout: Necessities are placed toward the back of the store. That requires shoppers to pass by everything else — all the fun and impulse buy items like computers and televisions to get to the milk and produce.

The Costco warehouse in Epping, Australia, shortly after opening. Costco Wholesale

Costco is nostalgic

Costco first opened in 1983 in Seattle and has "built its franchise with an older American affluent consumer," largely the baby boomer generation, Underhill tells CNBC Make It. In 2017, the most recent year Costco has data for, the average household income of the Costco member was $92,236. And because it is so popular with baby boomers, (those born between about 1946 and 1964), it has now become nostalgic to their children and grandchildren, aka millennials. "I've spoken to a few consumers that have started their relationship with Costco not so long ago and several of them recall the Costco experience with their families — shopping trips, eating in the food court, items at home — and so for them to now go back and have their own membership also almost becomes a rite of passage," says Hong. When you hated #costco trips as a kid. And now BEG your parents to give you in on their membership or at least take you for a shopping trip there. #adulting #graduation is too real Costco plays on the nostalgia because it's great branding: Take for instance, Costco's $1.50 Kirkland hot dog and Pepsi soda combo that has been available at that price since 1985, which industry tracker Winsight Grocery Business calls "Costco's secret weapon." "It's legacy. Look at all the people talking about it. ... It's one of the things we are known for," says Nelson. In fact, that's why it has the same price it did in 1985; Costco makes "very little money" on the combo deal, Nelson says, but "we get so much more mileage out of it than we would by raising the price to $1.60 and making a few more million dollars."

Costco's increasing investment in the e-commerce space is also playing well with younger shoppers, Hong says.

How it all boosts Costco's bottom line