When you talk about sentiment, you know it will reverse but you do not know when it will change. The news was very good today.

It's a very good way to start the year.

The markets today were not good at all, the markets are terrible,

We saw really good news to start the day.

Any little signal like this can lead people to sell first and to think about it later ... and it's partially a response to nervousness over whether the good times can continue,