There was a gigantic wall that protected a city from outside invaders. Children would play on this wall. They would enjoy taking stones and pieces of the wall and throwing them, seeing who could throw the farthest.
A man of the city noticed this and realized that even though the children are only taking a few stones every now and then, eventually this would cause a weakness in the wall and endanger the entire city.
So he rushed to the townspeople and told them this, but the townspeople laughed at him.
“These are children taking small stones! Don’t you see how gigantic this wall is? A small stone taken from it is like a drop in the ocean! It would take a thousand years for these children to make a dent. Stop being overly dramatic.”
So the man was ridiculed, but of course he was right. A small piece of wall means nothing by itself, but the nature of walls are that there is a cascading tendency where small changes can snowball into bigger effects in ways that cannot be anticipated or predicted beforehand.
And one day the wall collapsed, leaving the city vulnerable to attack which invading marauders took no time to take advantage of. They raided the city and left nothing in their wake.
The lesson is: Kids ruin everything! Keep those monsters on a leash!