Remember   product design is about making things that people want to own, enjoy
and with which they feel comfortable.   
At the end of a period of time even the best and most successful products need to be changed a little -  Perhaps just to revitalise a sagging market response or perhaps to improve the efficiency with which the item is made.  Perhaps the changes are necessary for some safety reasons  that have come to light whilst the product has been in use.

So, ask yourself lots of ways to improve any specific item that you use every day - and then set about suggesting ways that it could be improved.  Imagine why the manufacturer would want to change features of any design and would those changes be cost-effective and secure revitalised sales ?

Such proposals really define the start of doing the whole thing again !  Although the main consideration that stops constant change is economy of production.

So one product design is simply the end of one stage of the product's life span.
It may only be the 'end of the beginning'  if the company gets everything right.

Thanks to Dee Conroy for asking for some clarification on these points.
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