This is the 6753rd most frequent Chinese word.
殊不知
"Unbeknownst to" or "little does one know."
The phrase '殊不知' is used here to introduce an unexpected or unforeseen situation, negating the subject's assumption.
他以为自己赢定了，殊不知比赛才刚开始。
He thought he was sure to win, but little did he know that the competition had just begun.
Here, '殊不知' serves to highlight the unexpected duration of the rain that the tourists had not anticipated.
殊不知这场雨将持续一整天，游客们却没有准备雨具。
Little did they know, the rain would last all day, and the tourists were unprepared.
In this sentence, '殊不知' introduces a subtle contradiction to the belief that a solution had been found.