Everybody wants some...
So if you meet me
Have some courtesy
Have some sympathy, and some taste
The Rolling Stones - Sympathy for the Devil
In a chapter called "What Everybody Wants" Dale Carnegie supplies this answer: Be sympathetic with the other person's ideas and desires. You might want to jump right in and talk about a new business proposal, but if your client just got off a red-eye flight they probably won't be receptive. And if the tables had been turned, nor would you. Understanding the idea that, if we were in the other person's shoes we would likely act much the same way, can go a long way in winning over critics.
Carnegie says "The only reason you are not a rattlesnake is that your mother and father weren't. You deserve little credit for being what you are - and remember, the people who come to you irritated, bigoted, unreasoning, deserve very little discredit for being what they are." Craig Playstead notes: "to charm someone, you first need to disarm them. They need to feel that you’re not going to attack, criticize or berate them."
Surely it is not a coincidence that Expelliarmus, the incantation that in Harry Potter novels is used to disarm an opponent, will not only cause them to drop their wand (weapon) but will occasionally literally sweep them off their feet. It is not called the "disarming charm" for nothing.
Carnegie describes many ways to form a sympathetic bond with people. Most importantly, become genuinely interested in what others offer. Smile. Listen. Speak in their terms. And be agreeable. In addition to smiling, eye contact and body language can go a long way toward forming the correct bond. Consider this breakdown of Bill Clinton's charm.
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Just give it a try the next time someone tells you off while waiting in line, or online via social media for that matter. Instead of becoming defensive, disarm them with a smile and an apology. Have some sympathy, and some taste. If it doesn't sweep them off their feet, it will likely bowl them over.