PHY.2:2 - Problem

A resemblance can suggest an analogy while leaving the source unable to produce the behavior that matters. Two components that behave appropriately in isolation can behave differently when connected. A source can also reproduce one target observation through a mechanism that gives a different response to an intervention.

The difficulty is building the source itself. Its components, interactions, preparation and surroundings must jointly produce a useful consequence. When the target mechanism is unresolved, construction and criticism of the source also refine the hypothesis about the target. An unsuccessful source can expose the missing interaction or a physical restriction that the next attempt must address.