"Marketing Myopia" by Theodore Levitt.
Is a good, thought provoking piece of around 14 pages which can often be found in anthologies of marketing articles.
It is mentioned here as someone asked what my favourite marketing article was.
Surprisingly, this 36 year old bit of writing might be the reason why so many businesses are rushing onto the net!
Or custserv&hbsp.harvard.edu for a volume deal.