If you can measure it, you can manage it, goes the old adage. Partly, that's why email marketing is so successful. If your success rate is only 2 percent, you just send more. For larger campaigns, you have people who manage the email campaign, the A/B testing, the design, and all of the marketing automation. Digital marketing can be a big, expensive proposition, and not necessarily effective, as you can see in some recent epic ad fails.

Massive digital approaches may be wrong for some sales processes, suggests Cornell researcher and assistant professor of organizational behavior Vanessa K. Bonds in her new study published in the Journal of Experimental Psychology.

Her study of the success rates of 45 would-be sales people shows even when you communicate with a complete stranger, asking face-to-face is significantly more effective in getting to yes than asking in email, even when you use exactly the same script. How much more effective?

Asking in person is 34 times more effective, the study showed.

"You need to ask six people in person to equal the power of a 200-recipient email blast. Still, most people tend to think the email ask will be more effective," wrote Bonds in a recent Harvard Business Review recap of the study. She urges people to think about how much easier it is to ask six people in person than blast out 200 emails, and to use metrics-based judgment instead of personal estimates.

So why do we think email will be more effective than it is?

Bonds suggests one possible explanation is, as the email writer, we anchor emotionally on the legitimacy of what we're asking for, whether it's a donation or a sales demo. But the receiver, going about her own busy day, not only has an attention challenge but also may find an email from a stranger with a link a bit suspicious. The bar is going up for email, whereas for face-to-face requests, trust is built quickly as is merit. Plus in person, you can grow influence in person, which can have a lasting network effect. "It is often more convenient and comfortable to use text-based communication than to approach someone in person, but if you overestimate the effectiveness of such media, you may regularly--and unknowingly--choose inferior means of influence," she writes.