Be out of (one's) depth phrase
To be in a state of affairs that is too difficult for you to handle or comprehend.
I am a monolingual person. Therefore, when he asked me in a foreign language, I was out of my depth.
At that time, I was only able to ride a bike, so when he told me to ride a motorbike, I was out of my depth.
This expression alludes to being in water so deep that one might sink. It dates from around 1600.
The associates of public figures must not be suspected of being a part of any impropriety.
After being fired due to my brother's inappropriate behavior in the public, I finally understood the saying: "Caesar's wife must be above suspicion."