Analysts and investors had been predicting — and, in some cases, hoping for — Mason's departure for months now. Following a dismal fourth-quarter earnings announcement Wednesday, the company's board showed its co-founder the door.
"The only surprise here was that it took as long as it did to boot him," Sucharita Mulpuru, analyst at Forrester Research, said via email.
"Executive Chairman Eric Lefkofsky and Vice Chairman Ted Leonsis have been appointed to the newly created Office of the Chief Executive, effective immediately, replacing Andrew Mason," the company said in a statement. The two will serve as interim CEOs until a replacement for Mason is found.
"On behalf of the entire Groupon Board, I want to thank Andrew for his leadership, his creativity and his deep loyalty to Groupon," Lefkofsky said in the statement. (The peculiar, precise severance package, which also includes roughly six more months of health insurance, was at Mason's own request.)
In his typical oddball style, Mason dispensed with bland corporate-speak: "After four and a half intense and wonderful years as CEO of Groupon, I've decided that I'd like to spend more time with my family. Just kidding — I was fired today," he wrote in a memo posted online. "If you're wondering why... you haven't been paying attention."
Groupon never lived up to its $20 IPO share price after it went public in November 2011. Following the news on Wednesday of an $81.1 million net loss for the fourth quarter, its stock dropped 24 percent.
The company just got too big too fast, Mulpuru said. "They'd been set up for failure from the beginning. We'd been saying all along that there were only so many ways that you could goose up your revenue story before it caught up with you and finally it has."
(Read More: NBC News: Groupon Fires Founder, CEO Andrew Mason)
"I think his vision was correct, but you have to hold [Mason] culpable for the challenges it faced and the pressure on operations from international results," said Tom Forte, an internet analyst at Telsey Advisory Group. "In hindsight, the rapid pace of expansion both domestic and overseas created a business that was challenging to manage."
Groupon also was dogged by accounting fumbles, both in the run-up to as well as after its public debut. Miscalculating how much it had to set aside for customer returns forced the company to restate its first quarterly results as a public company, which prompted a preliminary SEC probe.
Last July, Evercore Partners analyst Ken Sena raised concern that a growing part of the company's revenue came from the lower-margin business of selling discounted products through its Groupon Goods program. "Given that first party sales transactions assume inventory risk in addition to driving higher revenue contribution, as they are booked gross vs. net, we see the need for greater transparency," he said at the time.
(Read More: Andrew Mason Out as Groupon CEO; Shares Jump)
Mason was certainly part of the problem, with a penchant for self-sabotage that undermined investor confidence in his leadership abilities: At one company event attended by reporters, he memorably swigged from a beer and joked about overindulging while exhorting employees to be more disciplined.
What comes across as quirky in start-up culture can telegraph as inexperienced or immature on Wall Street, and Groupon's stock suffered from Mason's antics.
"He just really never fit the type of a major corporate CEO," said Timothy Judge, a professor of management at the University of Notre Dame. "So when people see such poor performance... they have trouble finding any reason to have faith."
Judge said Mason's unpolished delivery of bad news also contributed to his fall. "We like that think we live in a world where if you're direct and open and honest that's the way it should be," he said. "I think the reality is his honesty ended up being used against him," because investors associated Groupon's performance with Mason's.
Even without Mason, Groupon has an uphill climb. "In the next couple of years, if they don't do something else, I fully expect" the stock to become worthless, Rocky Agrawal, principal analyst at Redesign Mobile, told CNBC on Thursday.
A new CEO can bring much-needed gravitas, but will face the same big-picture problems that bedeviled Mason. "The same challenges of slowing growth in daily deals is still there. A new CEO cannot change the market," Edward Woo, senior research analyst at Ascendiant Capital Markets LLC, said via email.
While Mason's replacement might be able to execute the vision of Groupon as a local e-commerce platform its founder was unable to put into action, Woo said it remains "a tall task for anybody."
"I think they should shrink and focus on the areas that are profitable," Woo said. "They should also face the possible option that their market opportunity is much smaller than they originally estimated."
Mason did offer one final piece of advice in his departure memo, after a tangent comparing his tenure to a notoriously hard video game: "[H]ave the courage to start with the customer. My biggest regrets are the moments that I let a lack of data override my intuition on what's best for our customers."
Just figuring out who that is would be a good first step. "Groupon needs to really decide who is their customer," Mulpuru said. "They've been acting like the shopper matters more. But that's what got them into this mess in the first place. They need to put the merchant first."