Hindsight bias

Sch bk 1, LOS 8d, Pg 193

In hindsight bias it says

‘They also overestimate what could have been known’.

I am unable to put it in a context.

Can someone please help me understand with an example.

Thank you

Coca Cola announced that they are brining out a range of beer. There stock price goes flying up.

There was no indication from any source that this was coming but yet the Investor is kicking himself as he feels he should have known this = Hindsight bias