When I was a kid, radical political activism was cool. By age fourteen, I was heavily involved.
But no matter how much you did, there was always this classic dilemma of "Hey, I'm only one out of six billion! And so is the guy next to me. It just does not seem plausible we could really make a difference!"
It didn't matter that you saw with your own eyes how much could be accomplished, that you had case histories to demonstrate how one person could turn around an entire world. It's a matter of cognitive dissonance --something
the human mind simply cannot accept until some explanation is given.
The Rebbe gave an explanation: My problem was that I was only looking at the physical, observable world, but not what's behind it --somewhat analogous to seeing the control panel and not the engine. Sure, the deed is something that happens in the concrete, mundane world, but where there is a heart and soul
behind the deed, then there is an effect deep within the metaphysical bowels of the natural order. So, just as one small button can trigger global reaction, one small deed can generate earth-shaking results.