One

It takes only one, they say. One of the matchsticks in a box to be lit, and the whole box to be on fire. One rotten apple in a basket to infuse the rest with its decay. One domino to initiate a series of falls, one piece after another. One mosquito in the middle of the night to disturb a restful sleep. One dense person to see two people leaving a hotel together to spark rumors. One selfish being to make many others miserable. One to sow chaos. 

Yet it takes only one piece of the jigsaw puzzle, too, to complete a picture. One candle lit to invade the darkness in one moonless night. One squeeze of lemon to balance out the salt and fat in butter. One kind person to see through you and your heart. One to plant the seeds for many others to harvest from which a tree grows. 

Just one, to either wreck or steady a ship. Imagine the value or the waste of one.