square peg in a round hole

Translations
человек не на своем месте
He felt like a square peg in a round hole at his new job.
Он чувствовал себя не на своем месте на новой работе.
Definitions
A person or thing that is unsuitable for a particular situation or role, often due to a mismatch between their skills or characteristics and the requirements of the task or environment.
Words
hole

noun
дыра
peg

noun
колышек
round

adjective
круглый
square

adjective
квадратный