John Wanamaker said it to illustrate how difficult it is to reach potential customers using traditional advertising: "Half the money I spend on advertising is wasted; the trouble is I don't know which half."
What I think he was looking for was Closed-Loop Marketing, but the idea was not presented publicly until the 1960s. What we've learned is that knowing what's working requires discipline to implement strategies, tactics and tool that support the quest for real ROI; the trade-off see most often is "Pay & Pray" - a common tactic that involves shooting from the hip, paying for advertising and praying it creates new customers somewhere down the line.
The good people at FohBoh have allowed me to create the group and offer up the conversation to fellow FohBoher's (or is that FohBOh-ites?) In this new group, we explore tactics, discussing the philosophies behind closed-Loop marketing and hoping to make restaurant marketers better at what they do - get butts in seats! Come join with us in the conversation!
Disclaimer - I love this stuff! I wrote 'ROI of Social Media', which focuses on this tactic quite a bit and I work with ProfitStreams in Denver, who is developing a platform that is translating the philosophy of Closed-Loop Marketing into code.
Link - Join the Closed-Loop Marketing FohBoh Group here - http://fohboh.com/group/closed-loop-marketing