We've talked before about how start-ups needing investment have been massively overestimating how quickly self-driving cars will become a mass-market reality. Add to that an overenthusiastic media, and you now have a general public that thinks their cars will be driving them to work early next decade. The major automakers haven't been immune to this as they will have to be in the game one day, but Mercedes' parent company, Daimler, has just realized it's going to be later rather than sooner. The company is also questioning the reality of a business model based around "robotaxis."

"There has been a reality check setting in here," Daimler AG Chief Executive Ola Kaellenius told journalists in a report from Reuters.

The idea of fleets of autonomous taxis ferrying people around cities is starting to become the tech industry's equivalent of turning lead into gold. The race started with Google back in 2012, but the vehicles will need to operate flawlessly day in and day out, all year, every year. Guiding cars around limited environments has become possible in public settings, and is relatively safe now. Still, autonomous vehicles need to be able to account for everything from the weather to random pedestrians, joggers, and cyclists. However, we've already seen accidents, including a self-driving Uber prototype kill a pedestrian in Arizona.

Kaellenius spoke about how Daimler's engineering team has found it more challenging than expected to develop self-driving cars. That will boil down to the last ten percent of development and software and hardware being able to anticipate the movement of anything that moves around the cars, no matter how random.

There's also the business model of autonomous taxis to consider. "The full-scale deployment would tie up a lot of capital with some uncertainties around the earnings potential," Kaellenius said. "At this juncture, we said to be the first one, does not make sense."

Considering the amount of money Daimler has already sunk into its autonomous projects, that's quite a blow. Executives will just have to wait longer before firing their S-Class chauffeur.