In his insightful article Jeff Weidauer writes that if you query the term "purchase funnel" on Wikipedia, and you'll find that it has its roots way back in 1898 with the so-called AIDA concept. AIDA stands for awareness, interest, desire, and action; those terms were the basis of what many classically trained marketers know today as the purchase funnel. That model stood the test of time, until the advent of the "path to purchase" model in the late twentieth century.
The problem with both the funnel and the path is the linear progression these models demonstrate for shopper behavior. We humans don't think in a linear manner any more today than we did a century ago, although we like to believe we do. The fact is that the path to purchase is not some "yellow brick road" to sales and profits; it's a convoluted journey with twists and turns and backtracks that more than anything resembles the flight of a drunken housefly.
There is little doubt that the journey from awareness to purchase has gotten much more complex in the past 20 years or so. Today we research everything from cars to movies to toothbrushes before spending any money - read more here