When a bochur returned from Merkos Shlichus disheartened having reached relatively few people, he shared his disillusionment with the Rebbe, who responded with three points.
The Merkos Shlichus program, in which a pair of bochurim scout an area for Yidden, planting seeds for Yiddishkeit, was established in 5703 under the Frierdiker Rebbe, and was expanded over the years.
One such bochur, after doing the Merkos Shlichus work over the summer of 5719, was disheartened with how relatively few people were reached. He shared his disillusionment with the Rebbe.
The Rebbe’s response, which included three points, “all of which are accurate,” was recorded by the Rebbe’s mazkir Harav Chodakov in his personal notes:
1) Sometimes one person who was inspired reaches out to another. This is called a chain reaction.
2) In a more successful scenario, a person of greater character can be influenced. If this person begins to be active with his own talents, an explosion can occur, like a spark reaching a barrel of gunpowder.
3) Besides for the above, it is an explicit halacha in Rambam: One must value one mitzva as if this one deed can tip the scale for the entire world.
(Hiskashrus 631)
From The Weekly Farbrengen by Merkaz Anash
In the summer of 1969, Yiroel Meir Popack O”H & I were on Merkos Shlichus traveling thru the South.
After spending time in Nashville and then Memphis our next stop was Little Rock Arkansas.
When I called ahead I was informed that only three out of ten people on our list were in town, so I called Rabbi Chodakov to ask him was it worthwhile to drive all the way to Little Rock for three people or should we skip it and go on to our next destination in Mississippi.
His Response: America just spent 1 billion dollars to send three people to the Livoneh and there isn’t even one Yid there.
For three Yidden, of course you should go.