Elon Musk has admitted developing autonomous cars is harder than he thought, as the timeline for the latest software update slips again.

Like most automakers, Tesla is working hard to crack autonomous driving, widely seen as the next big evolution for the auto industry. The company’s software has been criticized for being ‘easily tricked,’ and there have been several high-profile deaths involving Tesla’s Full Self-Driving (FSD).

When a user poked fun on Twitter over the latest software update missing its deadline, Musk responded, acknowledging the difficulties involved.

Musk’s admission underscores the challenges companies are facing in their effort to bring the auto industry into the future.