Say that a ball is sitting in front of a compressed spring launcher. The spring is then released. The spring applies a force on the ball for a certain distance. This force is accompanied by an equal and opposite force from the ball. Thus, the spring does some work $W$ on the ball, while the ball does exactly $-W$ work on the spring, correct? So, work is transfer of energy and always accompanied by a negative work on behalf of what is gaining kinetic energy, right?