The most important digital (consumer behavior) idea is…

Is this:

People who normally buy 1 book a month offline, when introduced to online, buy 12 books in 3 months, then stop buying for 9 months.

This happens because interactivity reduces friction. Reducing friction compresses the LifeCycle, resulting in the relative value of the customer being "exposed" more rapidly. 

Implication – You can design your entire digital marketing strategy based on this single idea (Recency). Yes, it's that powerful. Bet you didn't think digital was only all about SEM/SEO/Social.

This is such a profound insight. There's no way I could have come up with something like this on my own. Hate to reveal the source. Found it here.