Ok, just a quickie.
How do you explain the rise of the buzz-, viral and word-of-mouth marketing fads except through herd-like means?
Of course, you could look at the external factors influencing any one decision-maker (like there is such a thing!).
And you could try to understand the underlying disposition, marcom preferences and cognitive processes of the individual decision-maker. You could even look at how the individual saw their needs being matched by the offering.
But isn’t it easier (whatever they tell you) to see that folk are doing this stuff because other folk are doing it. Of course, there are some pioneers (matches and match-lighters) but the real mechanism behind the spread is other folk and what they do.
Just a thought.