Reb Dovid Goldwasser related a story that happened to him personally:
As I walked down the street one morning, deep in thought, I looked up momentarily to get my bearings. As I did, I saw a neighbor approaching from the opposite direction with his head bent toward the ground. He seemed troubled and withdrawn as I greeted him with a warm “Good morning.”
He glanced at me but didn’t reply. I felt I had to add something more, so I brightly said, “How’s your avodas ha’kodesh?”
His head snapped up briefly, in shock, as if I had said something wrong. He then quickly lowered his eyes back down and silently walked past me. Perturbed that I had perhaps (unintentionally) offended the man, I thought to myself that if only one could more often remember to follow the dictum of our Sages, “Siyog l’chochma shtika — Silence is a protective fence for wisdom.” But, I sadly concluded, the words had already been spoken.
The program of the day that ensued became exceedingly hectic, and eventually the morning encounter slipped my mind. When I returned home late that evening, I got the message that the man I had met in the morning had called and would be trying to reach me again. I speculated that he had been so upset by my remark that he had found it necessary to pursue the matter with a call.
When we finally spoke, the man launched into a personal narrative. He told me that he was a fundraiser for a Jewish communal organization, and the past year had not been very productive for him. In fact, the funds he had raised were less than his salary, and he just didn’t feel it was proper to be recompensed. As he walked by me that morning, he had been on his way to hand in his resignation.
Feeling sorry for himself, his self-esteem was in the dumps, and feeling quite miserable, my question had blown him away. He couldn’t believe that somebody actually framed his work in the realm of avodas ha’kodesh. He didn’t think anybody cared about what he did for a living. Like a bolt of lightning, my words struck him to the core, and he wondered if I was a heavenly messenger — a sign from Heaven. Suddenly, he felt revitalized and reenergized, and he decided to give his assignment another go.
In the end, that day turned out to be a very successful one; he raised more money than he had the entire year. He had called just to let me know the beneficial effect of my casual greeting.
You can never gauge the consequences of your words.