What is it?
The fallacy of composition occurs when someone assumes that what is true of the parts of something must also be true of the whole. It incorrectly transfers attributes from individual components to the entire system.
Examples
Person A: 'Each player on the team is an excellent athlete, so the team must be excellent.'
Person B: 'Each part of this machine is lightweight, so the entire machine must be lightweight.'
How to Avoid This
Remember that systems and wholes often have properties that emerge from the interaction of parts, not just from the parts themselves. Consider how components interact and whether properties scale linearly.
How to Counter This
Explain how the whole differs from the sum of its parts: 'While each individual component has that property, the whole system behaves differently because of how the parts interact.'