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.
Said when you are frightened to do something again because you had an unpleasant experience doing it the first time
After being cheated by her husband, Jane loses her belief on marriage and doesn't want to start any new relationship - a scalded dog fears cold water.