A cart of mass \(M\) carries two runners, each of mass \(m\), and is initially at rest on a frictionless horizontal track. If both runners jump off opposite ends of the cart simultaneously with identical horizontal speed \(u\) relative to the cart, the cart remains at rest. However, if the first runner jumps to the left with speed \(u\) relative to the cart, and subsequently the second runner jumps to the right with speed \(u\) relative to the cart, the cart acquires a non-zero final velocity directed to the left. Which of the following statements best explains why the cart moves to the left following the sequential jumps?