All people in a kingdom were asked to bring one glass of milk to be given for community welfare.
Someone thought, everyone else is going to bring milk only. Why not I carry water instead?
The day finally arrived. Not one, not two, rather all people had brought water.
Now let’s say everyone else was expected to bring water yet you carry a glass of milk this time.
The pond then created has veryyy little quantity of milk however everyone is going to consume this milk-water mixture.
Is there a chance that more people will bring milk next time? Is there a chance that this virtuous cycle will continue? For sure.
You don’t know what someone else will bring. You do know for sure what you will bring and how your micro actions affect the world at macro level.