From a wonderful book called "Sacred Therapy" by Estelle Frankel:
"Once, while on the road, Rabbi Isaac of Vorki and his teacher, Reb David of Lelov, stopped in an unfamiliar town. Suddenly a woman approached Reb David and began to beat him, having mistaken him for her estranged husband, who had abandoned her and her children several years earlier. While screaming and hitting Reb David, the woman suddenly realized that the man she was beating was not her husband but a famous Hasidic rebbe who happened to look a lot like her husband. Completely mortified, she immediately began to beg the rebbe's forgiveness, apologizing profusely for her terrible mistake. Instead of getting angry, Reb David responded with words of comfort, saying, 'It's OK, don't worry; it wasn't ME you were hitting....'"
If I am not for myself, who will be for me? If I am only for myself, what am I? If not now... when? --Hillel