The product life cycle is a tool for mapping out the four stages of a product’s commercial life: Launch, Growth, Maturity, and Decline. By understanding the life cycle of a product, designers and companies can make strategic decisions about the product, such as when to introduce a new version, or what types of technical innovations might be included. 

Why have a cycle? 

The reason is that society accepts products at different rates, but all go through similar stages of societal acceptance. This acceptance of innovations by societies is called the diffusion of innovations. As society begins to adopt and accept an innovation, the new product grows, eventually reaching maturity. When there is a better alternative to the product or when public preference changes, the products will enter a decline, possibly ending with the death of the product.

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The Product Life Cycle has four stages. Each stage is not determined by age, but by the relationship of sales, costs, profits, and number of competitors.

It is possible to predict the length of the product life cycle. For example, most digital devices produced today have quite short product cycles.It's common for most device manufacturers to introduce a new product every year. This is largely a result of technological advances proceeding at a predictable rate. 

However, consumer trends in fashion are quite unpredictable. This means that the product lifecycle can be shorten or lengthen unexpectedly.

A company can maintain a pioneering strategy and consistent revenue phone by introducing new versions of a product to market. A good example of this is smartphone manufacturers who regularly and consistently deliver new upgraded and updated versions of their product market.

Product versioning refers to the creation of variations of a product, different models, that are sold at different prices. 

This allows consumers to choose a product based on either its degree of function or its cost. The advantages of this strategy is that consumers can choose a model that suits them best. It also maximizes the profits for the company as they can target a larger market band.

A product becomes outdated as a conscious act either to ensure a continuing market or to ensure that safety factors and new technologies can be incorporated into later versions of the product.

Planned obsolescence artificially limits the useful life of a product. Designers have a moral responsibility to consider and reduce the environmental impact of their designs.

The artificial limiting of lightbulbs to 1000 hours ensured a steady demand for replacements, despite much longer-lasting lights being available.  See the documentary trailer

A product might have its life artificially limited in order to ensure that it continues to perform at the expected performance level. Inkjet printer manufacturers often point to this reason to justify planned obsolescence.  In order for the paper prints to consistent quality, the manufacturers limit the number of pages that they can actually print. Critics of this strategy point out that this is not an environmentally sustainable  as there is still usable material in the ink cartridge. In 2017, the French government sanction (punished) the big printer manufacturers for this practice.

 When a new technology supersedes an existing technology, the existing technology quickly falls out of use and is no longer incorporated into new products. Consumers instead opt for the newer, more efficient technology in their products.

An example here is the replacement of the VCR technology with DVDs. As  DVD technology developed, and the cost of DVD players came down, consumers elected to moved towards exclusively using DVDs. And now, physical media like DVDs have been replaced by digital streaming services such as Netflix. 

Fashions and trends change over time, which can result in a product no longer being desirable. However, as evidenced by the concept of retro styling and the cyclic nature of fashion, products can become desirable again.