A mouse is a thief. / The mouse isn't the thief, the hole is the thief.

Opportunity makes the thief.  SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten.  Compare:

A hole makes a thief.   |   A lokh makht a ganef.   |   .אַ לאָך מאַכט אַ גנבֿ

SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten

אַ מויז איז אַ גנבֿ.

A moyz iz a ganef.

A mouse is a thief.

ניט די מויז איז דער גנבֿ, נאָר די לאָך איז דער גנבֿ.

Nit di moyz iz der ganef, nor di lokh iz der ganef.

The mouse isn't the thief, the hole is the thief.