Complementarity: Why Can One Capability Make Another More Valuable?

Complementarity does not merely mean that two things are useful. It means that increasing one capability raises the value of the other. A camera and tripod provide a simple example. A tripod cannot take a photograph, and a camera can work alone; during a long exposure, however, stable support makes the camera’s light-gathering capability usable, while the camera gives the tripod’s stability a purpose.

This is the opposite of substitutability. Substitutes can perform similar tasks, so having more of one reduces the need for the other. Complementarity is also not identical to synergy: synergy describes the combined outcome, while complementarity concerns how the value of each part changes in the presence of the other. That is why evaluating an investment in isolation can be misleading. Better equipment may add little if people are given no time to learn it. The useful question is not only how strong each capability is by itself, but whether it enables another capability to do more.