What a great quote
There have been a great many minds that have tortured themselves over pondering the things we don't even blink an eye at today.
We admire and idolize those who found the pretty pebbles that light up the shore today, and yet I'm sure many of them would have eagerly traded places just to see what continued to take shape.
It's sad, though also a reminder of just how much is easily taken for granted.
That business about pebbles is Newton showing off. Calculus is Latin for small pebble.
In fact, you can see hints of it even in this quote: “I don’t know what I may seem to the world” — suggests that he thinks of himself in an exalted position wrt the world (= other people, in this context), but a little boy wrt Nature. Something like: I am a little boy collecting pebbles on the shore, while everyone else is a senseless baby not even close to the ocean.