You've probably seen pics of Spider-man boxes sitting on shelves or flash sales trying to dump them on the cheap, but Wizards has said the set is a success. How can the same set be a smashing success and a huge flop? Let's talk about how the Magic market actually works.
Local game stores and other vendors have to place their orders for the set early (you know those super early spoilers we get every set, Wizards has said they are so vendors can figure out what to order, and vendors order shortly thereafter, months before the set release or is fully previewed).
As a result, game stores have to order based on how well they *think* the set will sell, basically making an educated guess. They order from distributors, who get the boxes from Wizards. As a result, the money for these boxes is in Wizards pocket months before the set even releases and it's locked in no matter how many boxes the game stores actually sell.
With a set like Spider-man, vendors ordered a lot of boxes because, well, Spider-man is iconic, Marvel is huge, and other sets were selling well. As a result, the set made Wizards a ton of money, but what we are seeing now - prices dropping, flash sales, overstocked shelves - is vendors struggling to sell the product to players.
Basically, Spider-man was a huge success for Wizards before they even spoiled the cards. Even if literally the entire Magic community refused to buy Spider-man, it wouldn't have an immediate impact on Wizards bottom line because they already got paid for all the boxes, it's the game stores and distributors left holding the bag.
However, this can hurt Wizards in the long run, because when it comes time for vendors to order Teenage Mutant Ninja Turtles or Marvel Legends they might not order as much after getting stuck with a bunch of Spider-man they couldn't sell. Basically, any negative impact wouldn't be reflected in Wizards bottom line from Spider-man (or any set, they all work the same) until future sets.
And that's how the same set can be both a smashing success and a huge flop, at least in the short term.