百思不得其解

bǎi sī bù dé qí jiě

completely baffled

Character by character

百bǎi
hundred

思sī
think

不bù
not

得dé
get

其qí
its

解jiě
explanation

他为什么突然辞职，大家都百思不得其解。

Nobody can work out why he suddenly quit.

Tone: neutral.

解 is jiě; often follows a question about why something happened.

Learn it in context

This idiom and thousands more are in Learn Chinese with Bao, with audio, pinyin and drills that make them stick.