I've written about Tesla's loose relationship with reality when it comes to what the company calls "full self-driving." For an additional $10,000, you can order a Tesla right now with that option, which the website describes as the ability to navigate on autopilot, change lanes automatically, park your car, summon your car, stop at traffic lights, and, eventually, auto steer on city streets. 

That sounds a lot like your car can drive itself. It's not. Of course, in the fine print, the same page says: 

The currently enabled features require active driver supervision and do not make the vehicle autonomous. The activation and use of these features are dependent on achieving reliability far in excess of human drivers as demonstrated by billions of miles of experience, as well as regulatory approval, which may take longer in some jurisdictions. As these self-driving features evolve, your car will be continuously upgraded through over-the-air software updates.

Really, it's more of a promise of self-driving at some point in the future. Which, to be honest, is still pretty cool. The problem is that Tesla's CEO, Elon Musk, has made a lot of promises about the company's autonomous driving program, almost none of which it has been able to keep.

Now, in a single sentence, Musk explained why:

"It's amazing by most standards, but we are aiming for 1,000 percent safer than the average human driver."

The explanation came in a tweet, as it often does with Musk. This time in response to a Tesla driver who seems very excited about the self-driving capabilities. It's worth mentioning that, compared with the average tweet from Musk--who has more than 50 million followers--this one generated very little attention. Still, it was pretty important. Here's why:

Just last week, Musk had said that the current beta of FSD wasn't very good, but that the company is working on it. This Tesla driver disagreed. "#FSDBeta v9.2 performing "great" despite @elonmusk claims," the tweet reads. 

In some ways, it's uncharacteristic of Musk, who has never been shy about showmanship. He's never been shy about overpromising, either. In this case, however, he explains how the company is approaching one of the most challenging technology problems--getting a car to drive itself more safely than a human can.

Making FSD 1,000 percent safer than the average human driver seems like a pretty difficult goal. I don't even know how you quantify that, but it isn't hard to see why it's taking the company some time. To that end, I'm sure Tesla has very smart people working on the problem.

The thing is, drivers have to have confidence that the company has solved the problem beyond any likely failure point. If the minimum expectation is that a self-driving car is at least as safe as a human, Tesla's goal is to go far beyond that expectation. 

This is actually a big deal, because the only thing harder than making vehicles that can drive themselves is convincing large numbers of people to actually trust their lives to those vehicles. That might be the hardest problem in technology, and it's the one Musk has to solve. Otherwise, all of the effort to build computers that can react the way humans do, and cars that can navigate themselves, will be for nothing.

Humans have been driving cars for over 100 years. While the experience has obviously changed over the past century, it still involves a driver with their hands on the steering wheel and their foot on the accelerator or brake. That doesn't necessarily mean it's the best way to drive a car, but it's certainly the one that most people are comfortable with. Whether they're actually safe is another question, but they certainly feel safer when they have control over their vehicle.

If Musk has his way, that will change soon. The vision for autonomous driving is that you simply get in, tell your vehicle where you want to go, and relax while it does the work. You could check your email or binge-watch Ted Lasso. That's a fantastic idea until you realize he's serious. Then, it's just terrifying. 

The only way most people are going to trust their lives to a fully self-driving car is if they believe it's safer than if they drive it. And not just a little safer, but 1,000 percent safer.