Just as a trickle of water can slice through stone, so, too, a consistent thought pattern eventually affects
one's soul.
When someone spends more than a few moments daily in his imagination-when one invests hours-little by little, his thoughts carve into the very essence of his soul.
On occasion, they may change him completely.
It is common knowledge that anthropologists and diplomats must occasionally return home from their research or embassy postings.
If they fail to do so, their environments become so deeply enmeshed in their awareness, and they identify with them to such an extent, that their missions are compromised.
More than one researcher has arrived at a distant locale to study an exotic people and, though mindful of its ways and superstitions, after too long a stay began to accept some of the indigenous beliefs, fears, and general mind-set.
The regular involvement with such matters, thinking of them repeatedly, the habitual attempt to imagine oneself in the other's place-all this influences the essence of one's soul.
Whether for a minute or even the blink of an eye, the impression is lasting.
–Rabbi Adin Steinsaltz
From Learning from the Tanya by Rabbi Adin Steinsaltz