Three engineering firms were competitively bidding on Red-Sea tunnel project for the government of Egypt. The first engineer stands before the board and begins describing how he will accomplish the task. He says, "We will begin boring from both sides of the sea and join the tubes in the middle. Our plan has 10% margin of error for missing the center point but we have B-plan ready to rectify the error and finish the tunnel."
Second engineer comes in and describes his plan. "We will begin boring on both ends and meet in the middle. Our calculations may have 5% margin of error and our plan B is ready to rectify and connect the tunnel if needed."
Third engineer begins his presentation and says, "We will begin boring on both ends of the sea and meet in the middle. If successful, we'll connect the tubes and you'll have your tunnel. If we are not, then you'll have two tunnels."