Oh dear, a fire breaks out!
In a room full of people (aka proteins), only 1 protein is responsible for saving the fire. So this protein takes a bucket of water, and rushes to put out the fire.
Or imagine another scenario
The protein responsible for putting out the fire contacts a few people in the room that are sleeping fire wardens… each fire warden contacts a few sleeping firefighters… the whole room of inactive people suddenly wakes up into action! The original protein simply needs to do one little thing… which is to activate the wardens, and each warden in turn does one small thing, to activate the firefighters… and finally the vast numbers of activated firefighters fights the fire!