Product development is cheapest when the design is still flexible. During the concept and prototype stages, changing a dimension, moving a feature, or testing a different material may require little more than updating a CAD model and producing another prototype. The same change after tooling has been built can trigger an entirely different chain of costs.
As a program advances, more decisions become connected to the design. Tooling is manufactured, suppliers establish processes, inspection fixtures are created, documentation is released, materials are ordered, and production schedules are built around the approved geometry. A seemingly minor revision can suddenly affect multiple systems at once.
This is why early iteration is so valuable. Simulation, rapid prototyping, tolerance analysis, DFM reviews, and cross-functional feedback allow teams to discover problems while modifications are still relatively inexpensive. Finding an interference issue or weak feature before tooling may require a simple design revision. Finding it during production could require tool modifications, new validation runs, updated documentation, and delayed shipments.
The goal is not to eliminate design changes. In fact, strong development programs encourage changes when information is still inexpensive to act on. The objective is to move uncertainty forward, testing assumptions and resolving critical questions before expensive manufacturing commitments are made.
Development speed should therefore not be measured by how quickly a team freezes its design. A better measure is how efficiently it eliminates uncertainty before that freeze. Iterate aggressively when iteration is cheap, because every unresolved problem becomes more expensive once physical tooling and production infrastructure depend on the answer.