R. Yissachar Dov of Belz once took his young son to immerse in the mikvah.
Initially, when the young boy placed his feet in the frigid waters he yelled out “oy oy.” However, after he exited and warmed up a bit, he said with satisfaction “ah ah.”
His father remarked: “My son, this is the difference between a mitzvah and sin. When one performs a mitzvah it begins with an ‘ay’ and ends with an ‘ah.’ However sin begins with an ‘ah’ and afterwards comes the ‘oy.'”
R. Moshe Pshevorsker remarked: “What is the difference between a mitzvah and sin? When someone performs a mitzvah they are happy when they complete it, however in sin, one is only happy before they do it.”