The story is told of two friends who, in their youth, were both the disciples of the same rebbe.
In the course of time, one became a commissar in the Communist Party, while the other remained a God-fearing Jew.
One day, they met, and the latter asked the commissar, "I wonder, does anything remain with you of all the years that we studied together?"
The commissar replied: "Sinning. I sin a lot, but I get no true satisfaction from it.”
–Rabbi Adin Steinsaltz
From Opening the Tanya by Rabbi Adin Steinsaltz