If there’s one noticeable sentiment emerging from Ford under the reign of newly-hired CEO Jim Hackett, it’s the company’s toward self-driving cars. The official line, lately, is: yes, this technology is Good and Will Happen, but it Will Take Time. More time than the thought leaders in Silicon Valley would have you believe.

That’s echoed in a by the CEO of Argo AI, a startup Ford has invested $1 billion in, and says there remains “significant work” to reliably bring the technology to the public.

The blog post from Argo’s CEO, Bryan Salesky, outlines a winding history over the last decade, and illustrates just how far the industry has come in a short amount of time.

Though he doesn’t name names, it’s hard to take this passage as anything but a shot at competitors who’re racing to deploy fully-automated cars as quickly as possible.

We’re still very much in the early days of making self-driving cars a reality. Those who think fully self-driving vehicles will be ubiquitous on city streets months from now or even in a few years are not well connected to the state of the art or committed to the safe deployment of the technology. For those of us who have been working on the technology for a long time, we’re going to tell you the issue is still really hard, as the systems are as complex as ever.

Ford itself has said it’d like to have self-driving cars on the road by 2021, but only for uses like ride-hailing or package delivery at first. Other automakers and tech developers have pilot projects already underway—Google’s self-driving car project Waymo is , and across the U.S. on its platform.

Automakers like Ford, Fiat Chrysler and General Motors have established partnerships with ride-hailing companies and autonomous tech developers to speed up the development of robocars, as well. Tesla CEO Elon Musk has said he’d like to send an autonomous car on a trip from Los Angeles to New York City by the end of this year.

But Salesky says there’s a number of lingering, significant barriers to making the technology works safely and efficiently. In particular, he writes, sensors aren’t nearly capable yet for fully-automated driving. That includes LIDAR, a laser-based radar short for that allows cars to “see” the road and is considered to be crucial for autonomous vehicles by most of the industry.

LIDAR can provide a 3D image of the world around a car, Salesky says, but it “doesn’t provide color or texture.” So you need cameras, as well. A lot of them, too. Redundancies are necessary to ensure there’s a failsafe in case one part of the technology fails.

Salesky goes on:

Yet cameras are challenged in poor lighting, and tend to struggle to provide enough focus and resolution at all desired ranges of operation. In contrast, radar, while relatively low resolution, is able to directly detect the velocity of road users even at long distances.

That’s why we still have so many sensors mounted on the car — the strengths of one complement the weaknesses of another. Individual sensors don’t fully reproduce what they capture, so the computer has to combine the inputs from multiple sensors, then sort out the errors and inconsistencies. Combining all of this into one comprehensive and robust picture of the world for the computer to process is incredibly difficult.

to help articulate how self-driving car should be tested. Still, the proposed laws seem to offer a mostly-hands-off approach. Automakers could deploy more robot cars that are exempt from certain regulations, but those cars need to be equipped with technology that works. The public just yet, so perfecting the tech is necessary for robotcars to be adopted en masse.

And that brings up another key point. Automated cars need a lot of experience on the road to understand their surroundings and to “drive with confidence.”

But not all miles are created equal, so “accumulated miles” is not an expressive enough metric to track progress. Think of it this way: The skills you acquired learning to drive in a quiet Midwestern town will not translate should you find yourself driving in the heart of Manhattan.

Will you see a fully-automated car on the road soon? Sure. California just approved regulations that will . But it’ll be confined to limited spaces. Salesky’s insight illustrates why that’s the reality of the situation. Don’t believe the hype.