it is hard to explain; it is hard to say
A set phrase used when something is difficult to put into words, often because it is complex, delicate, or beyond easy description. Has a slightly literary or formal feel.
My feelings at that time are hard to put into words.
The charm of his work is difficult to describe.
Common modern expression for 'cannot put into words'; more casual and direct than 曰く言い難し.
A set phrase combining 曰く “circumstances or underlying reason” with 言い難し, the classical terminal form meaning “hard to say.”