The Parable of the Two Watchmakers was introduced by Nobel laureate Herbert A. Simon to explain why hierarchical, modular systems evolve and survive better than tightly coupled ones. It illustrates how complex structures are built far more efficiently when broken into stable sub-assemblies.

The Story

There are two master watchmakers: Tempus and Hora.

• Both make extremely intricate watches, each containing 1,000 individual parts.
• A phone rings often while they are working, forcing them to stop frequently.

Tempus’ method (non-modular design):

• He assembles the watch piece by piece.
• If interrupted, the half-assembled watch falls apart.
• He must start over from scratch every time.

Hora’s method (modular design):

• He builds subassemblies of 10 parts first.
• Then he combines 10 of these to create larger assemblies, and so on.
• If interrupted, only a small module is affected — the rest stays intact.

Result: Hora produces watches much faster and with far less wasted work, even though he and Tempus are equally skilled.

Key Insights

• Complex systems are far more robust and evolvable when built out of smaller, stable, reusable components.
• Modularity is the key to building and sustaining complexity.
• Stable subsystems make complex structures more resilient.
• Interruptions (or disturbances, failures, shocks) punish non-modular systems but have minimal impact on modular, hierarchical ones.
• Systems that can “hold together” when disturbed will outcompete those that fall apart.