YOU SAID:
Arm is something that I will never understand
INTO JAPANESE
腕は私には決して理解できないものです
BACK INTO ENGLISH
Arms are something I can never understand
INTO JAPANESE
腕は私には理解できないものです
BACK INTO ENGLISH
Arms are something I don't understand
INTO JAPANESE
腕は私にはわからないものです
BACK INTO ENGLISH
The arm is something I don't understand
INTO JAPANESE
腕は私にはわからないものです
BACK INTO ENGLISH
The arm is something I don't understand
That didn't even make that much sense in English.