Slow vs quick

In the middle ages, there used to be a form of torture and execution  where they would lay a person down, and then place a large board on top of them, like a door. They would start piling rocks on top of the board.
They were not large rocks, and any one of them alone wouldn't have really done much  to hurt the person. Especially with the board distributing the pressure over the whole body.
But there were a lot of these small rocks, and they kept piling up. Eventually it would kill a person but it was very slow. And very painful.
I can imagine , at some point the person would wish for one large  boulder to  squish them quickly, rather than the pile of hundreds of small rocks.

 This form of torture is like life. Sometimes, if you only see one little pebble   piled on someone, you might not understand the person's reaction, because you don't know how many rocks came before it.  We never know how many rocks each person has already  squashing them down.
And  if you can ever lift a pebble off of someone, you might think it's so small it would never make a difference. But all those  pebbles add up.