Once the British parliament wanted to decide to introduce driving on the right side of the road, like the most of the rest of the world does. During the deliberations, one of the older lords said: "I agree that we should start driving right. But, gentlemen, we can't do this overnight. I propose that during the first year, only the lorries drive right."

Now why is this a programming joke?

Ever heard of "We'll use the old application in parallel for a while until we switch to the new one"? A time-honored recipe for disaster. Not always, though, but most of the time it makes deployment a nightmare, and conversion of the old data a recurring nightmare.