You wrote "isn't it arrogance (or even foolishness) for a few Nepalese to think they can work to make a difference?"

I am not sure if it was a real question or a rhetorical one.
If your father said those words, there's one attitude that this question would come from.
Your father's attitude and thoughts are, "Son, you think you are so great that you can make a big difference in Nepal (and the world)?"
Interesting.

It reminds me of the time my father scoffed at me when I announced that I was going to learn to play guitar. I was in my teenage rebellion phase and his scoff annoyed me quite a lot. I learned to play the guitar in a couple of weeks. After I could play a couple of rock songs, my dad was mildly ok with it. He was not a very music oriented guy so I don't blame him that much.

Small changes do matter. Your work will definitely not be in vain if you are sincere.
so yes, the drop in the ocean might seem like a drop but has the potential to be a driving force for change. There is of course no guarantee. It depends on your own intentions, hard work, sincerity and some luck too (probably).

A question to you now:
Do you think Nepal is worth saving?