The Product Life Cycle is not always Shaped like a Wave Form!

Variations on clean wave patterns
Philippe
Other reasons for disturbances of the wave form are also possible. Think of seasonal effects. Also the company itself can influence the pattern. For example by investing a lot in promotions in the maturity stage. Or by introducing product innovations.

Life Cycle form
Bertus
Also changes in the taste of customers and even such unpredictable external variables as the Euro or Dollar rate may influence the wave-form of the cycle.

Product Life Cycle not Symmetrical
Dr.P.L.Narasimhan
Please permit me to add few comments on this informative article on the product life cycle. Generally the curve is not symmetrical and short in X-axis after maturity. There is every likelihood that the curve may also stoop steeply after maturity because of the competitive pressure and change in technology. The mature stage may also be flat. The company should be ready with the next product ready to be released, based on the timing, and revenue realization in relation to the investment. Possibly the company can think of extending the life of the product by flattening the mature stage and lessening the drop in the decline stage by value addition to the product.

Distinguish between Product LC and Brand LC
Dr. Uditha Liyanage
A distinction must be made between the Product Life Cycle and the Brand Life Cycle. The PLC may follow a different trajectory from that of the BLC.

No Revitalising in the Maturity Stage
Sandeep Dogra
The Maturity stage is a honeymoon period for any product with a life span of minimum 7 years. It is accompanied by low advertising intensity, homogenous and large packaging, defined target market and above all a stable loyal cutomer base.
So watever be the revitalising strategies (Market Penetration or Product Development), they must be applied in the Decline stage.

Product life cycle profit vs volume
Mats
Another disturbing factor is that the actual product volume varies over time and the input and effort of the production system vary. Thus, it would be interesting to build on the curve and include profit margin.

The decline is the beginning of a new cycle.
Wilians Rizzo
The decline phase starts when a new product appears with more advantages.

Product Lifecycle Model
Dr Adrian Boucher
Although the general characteristics of the PLC model make use of the concepts of Introduction-Adoption-Maturity-Decline, there can be variations on this main theme. The overall profile of the PLC curve over time is most unlikely to be symmetric, because opportunities exist for prolonging the PLC through enhanced marketing activities (and budget), or of thinking of new uses for products. One classic example (possibly apocryphal) concerns the fate of baking powder (soda). As home baking declined from the 1950s-60s, sales of the product plummetted until an accidental placing of some baking powder in a refrigerator overnight killed unpleasant odours, rendering a brand-new life for baking soda as refrigerator deodorant and subsequent high profits.

Crossing the Chasm, Product Manager
Keita Gunji, Director, Japan, Member
In case of high-tech industry, we consider the diffusion of innovation(ref. 'Crossing the Chasm' Geoffrey A. Moore). Based on this, there's a gap to clean up skepticism for new technologies. And it'll take 6-month to 2-year period until the diffusion of innovation accepted into majority group. Company will take marketing action to cross the chasm existing between innovator and early majority. But sometimes, a product won't be able to cross the chasm due to investment issues, people issues, and market timing issues. Then most of them will not keep up with the PLC model, drastically change their business situation and their operation may get to the end or be targeted at M&A before success.
However, companies understand such a trend and then apply marketing activity to stabilize sales as well. Then in the long run, the product's life cycle doesn't misfit the general model. A product manager should control these scenarios.