Tesla CEO Elon Musk was arguably the biggest tech titan to speak at the 2017 TED conference .

During an onstage interview with TED curator Chris Anderson, Musk explained why he’s focused on underground transportation (through Hyperloop and his new tunnel boring company, the Boring Company) instead of flying cars.

According to Musk, the main challenges with flying cars are that they’ll be noisy and generate lots of wind because of the downward force required to keep them in the air. Plus, there’s an anxiety factor.

“Let’s just say if something is flying over your head…that is not an anxiety-reducing situation,” he said. “You don’t think to yourself ‘Well, I feel better about today. You’re thinking…’Is it going to come off and guillotine me as it comes flying past?’

Later in the interview, Anderson asked Musk whether other automakers were attempting to follow in Tesla’s footsteps with electric vehicles. “I think almost every automaker has some electric vehicle program. Some are serious about transitioning entirely to electric,” he said. “Apparently, in order to motivate BMW executives, they showed a picture of me.”

Here is a video of the TED conference: