Nicolas Cole says marketing isn't a guaranteed return on investment. It's more like a lottery: a series of bets where you test mechanisms and focus on the ones with the best odds of working.
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The biggest thing that people misunderstand about marketing is they think that marketing is a sure thing. They think the way you sell services is by going to someone and saying, "If you pay me a dollar, I will make you $3." I hate to be the bearer of bad news for everyone, but if you had your own lottery machine where you spent a dollar and you made $3, you wouldn't bother doing it for anyone else. You would just do it for yourself and then go buy a yacht. So all of marketing is speculation, all of it. And so your job is to find the marketing mechanisms that have the highest likelihood, the best speculation, and going, "We should try these."