A chassid once came to Rabbi DovBer, the "Maggid" of Mezeritch. "Rebbe," he said, "there is something I do not comprehend. When the Almighty commands us to do something or forbids a certain act, I understand. No matter how difficult it may be, no matter how strongly my heart craves the forbidden course, I can do what G‑d desires or refrain from doing what is against His will. After all, man has free choice and by force of will he can decide on a course of action and stick to it, no matter what. The same is true with speech. Though somewhat more difficult to control, I accept that it is within my power to decide which words will leave my mouth and which will not.

"But what I fail to understand are those precepts which govern matters of the heart; for example, when the Torah forbids us to even entertain a thought that is destructive and wrong. What is one to do when such thoughts enter his mind of their own accord? Can a person control his thoughts?"

Instead of answering the chassid's question, Rabbi DovBer dispatched him to the town of Zhitomir. "Go visit my disciple, Rabbi Zev" he said. "Only he can answer your question."

The trip was made in the dead of winter. For weeks the chassid made his way along the roads which wound their way through the snow-covered forests of White Russia.

Midnight had long come and gone when the weary traveler arrived at Rabbi Zev's doorstep. To his happy surprise, the windows of the scholar's study where alight. Indeed, Rabbi Zev's was the only lighted window in the village. Through a chink in the shutters the visitor could see Rabbi Zev bent over his books.

But his knock brought no response. He waited a while, then tried once more, harder. Still, he was completely ignored. The cold was beginning to infiltrate his bones. As the night wore on, the visitor, with nowhere else to turn, kept pounding upon the frozen planks of Rabbi Zev's door, while the rabbi, a scant few steps away, continued to study by his fireside, seemingly oblivious to the pleas which echoed through the sub-zero night.

Finally, Rabbi Zev rose from his seat, opened the door, and warmly greeted his visitor. He sat him by the fire, prepared him a hot glass of tea, and inquired after the health of their Rebbe. He then led his guest — still speechless with cold and incredulity — to the best room in the house to rest his weary bones.

The warm welcome did not abate the next morning, nor the one after. Rabbi Zev was the most solicitous of hosts, attending to the needs of his guest in a most exemplary manner. The visitor, too, was a model guest, considerate and respectful of the elder scholar. If any misgivings about the midnight "welcome" accorded him still lingered in his heart, he kept them to himself.

After enjoying the superb hospitality of Rabbi Zev for several days, the visitor had sufficiently recovered from his journey and apprehension to put forth his query. "The purpose of my visit," he said to his host one evening, "is to ask you a question. Actually, our Rebbe sent me to you, saying that only you could answer me to my satisfaction."

The visitor proceeded to outline his problem as he had expressed it earlier to the Maggid. When he had finished, Reb Zev said: "Tell me, my friend, is a man any less a master of his own self than he is of his home?

"You see, I gave you my answer on the very night you arrived. In my home, I am the boss. Whomever I wish to admit — I allow in; whomever I do not wish to admit — I do not."