The personal computer industry is in turmoil. Its downfall can be traced to a specific date in history and a brand new product category. On April 3, 2010, Apple(AAPL 0.53%) released the iPad. The upward trajectory in tablet shipments has coincided with a rapid decline in those of PC's. Tablet sales could top PC sales for the first time in 2015, according to one analysis.

One of the top players in the PC industry, Dell, recently went private after floundering for a number of years. Lack of viable alternative products to PC's probably had a lot to do with the decision.
HPQ Total Return Price data by YCharts
Standalone GPS device manufacturers had no competition in the turn-by-turn navigation market for over a decade, until Google and others added GPS capability to mobile maps apps.
Some tech inventions have turned entrenched industries upside down and affected investment decisions.