Yiddish: Understanding grows at a snail's pace.

Literal translation: Understanding (or good sense) is a slowpoke.
SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten.  Compare:

Understanding comes with age. | Der seykhl kumt nokh di yorn. | .דער שׂכל קומט נאָך די יאָרן

SOURCE: Furman, Yidishe Shprikhverter un Rednsartn

The truth is a slowpoke. | Der emes iz a krikher. | .דער אמת איז אַ קריכער

SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh

דער שׂכל איז אַ קריכער.

Der seykhl iz a krikher.

Understanding grows at a snail's pace.