Last night, or this morning, depending on where you are in the world, Tesla unveiled the new Robotaxi and Robovan.

There was a side effect that no one foresaw, but we should have.

The thing is, the 'buy the rumour, sell the news' mantra is real, and it applies to the stock market as well.

Less than two weeks ago, Tesla stock $TSLA was trading at around $260 per share.

It then went down to $240 per share and stayed there till the unveil, after which, it went down to $224 per share.

It's counterintuitive, in a way, because the Tesla event was arguably better than expected. Not one but two vehicles, and one was a lot better than people thought, and Optimus (the humanoid robot) is clearly showing progress.

And yet the stock went down.

But why are we surprised? That has always been the case since the internet was invented.