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Overengineering (or over-engineering) is the additional designing of a product to be more robust, extra featured than is deemed necessary for its primary application to be completed successfully or have an unnecessarily complex process that produces an outcome inefficiently. Either (charitably) to ensure a more than sufficient factor of safety, more than sufficient functionality limits, or to overcome potential design errors that are considered acceptable for most users expectations. Overengineering can be desirable when safety or performance on a particular criterion is critical (e.g. aerospace vehicles), or when extremely broad functionality is required (e.g. diagnostic tools), but it is generally criticized from the point of view of value engineering as wasteful both in materials and cost. As a design philosophy, such overcomplexity is the opposite of the less is more school of thought (and hence a violation of the KISS principle and parsimony).
Overengineering generally occurs in high-end products or specialized market criteria, and may take various forms. In one form, products are overbuilt, and have performance far in excess of expected normal operational limits (a family sedan that can drive at 300 km/h, or a home video cassette recorder with a projected lifespan of 100 years), and hence are more expensive, bulkier, and heavier than necessary. Alternatively, they may become overcomplicated – the extra functional design may be far more complicated than is necessary for its typical use, such as a business office text editor asking whether files should be saved in ASCII, EBCDIC or various multi-byte formats used almost exclusively by engineers and not business. Overcomplexity could overwhelm most typical users and potentially reduce the usability of the product by most end users, and can decrease productivity of the design team due to the need to build and maintain all the additional features.
A related issue is market segmentation – making different products for different market segments. In this context, a particular product may be more or less suited for a particular market segment, and may be over- or under- engineered relative to an application.
A story about very precise engineering is given in the 1858 story The Deacon's Masterpiece or, the Wonderful "One-hoss Shay": A Logical Story by Oliver Wendell Holmes, Sr., which tells of a carriage (one-horse shay)
That was built in such a logical way
It ran a hundred years to a day,
went to pieces all at once, --
All at once, and nothing first, --
Just as bubbles do when they burst.
Because it had been engineered so that no single piece failed first – no piece was over-engineered relative to the others, and they thus all collapsed at the same time.