There is a formula that applies to almost everything and it is called reversion to the mean, also regression to the mean.

有一个公式，适用于几乎所有的东西它被称为回归的意思，也均值回归。

youdao

As far as bearish sentiment rising, it may simply represent a reversion to the mean.

FORBES: Bulls Slip But Don't Fall

There is a reversion to the mean return, but it requires a long enough investment period to revert.

FORBES: The Efficient Frontier

The rebound in pessimism was a reversion to the mean for bearish sentiment, which signals that worries about the economy have not faded.

FORBES: Optimism Slips Slightly, Pessimism Rebounds