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From a strictly logical point of view, the colleague is being irrational. The brother-in-law's bad Volvo experience is a single data point swamped by tens of thousands of good experiences--it's an unusual outlier. But we are social creatures. We are easily swayed by first-person stories and vivid accounts of a single experience. Although this is statistically wrong and we should learn to overcome the bias, most of us don't. Advertisers know this, and this is why we see so many first-person testimonial advertisements on TV. "I lost twenty pounds in two weeks by eating this new yogurt--and it was delicious, too!" Or "I had a headache that wouldn't go away. I was barking at the dog and snapping at my loved ones. Then I took this new medication and I was back to my normal self." Our brains focus on vivid, social accounts more than dry, boring, statistical accounts.