Evolution has given us a brain with what scientists call a "negativity bias," which makes it prone to feeling threatened. This bias developed because the early humans who were mellow and fearless and who did not notice the shadow overhead or the slither nearby are the ones who got chomped. The ones that survived to pass on their genes were nervous and cranky, and we are their great-grandchildren, sitting atop the food chain.
Your brain is continually looking for bad news. As soon as it finds some, it fixates on it with tunnel vision, fast-tracks it into memory storage, and then reactivates it at the least hint of anything even vaguely similar. But good news gets a kind of neutral shrug: "Eh, whatever."
In effect, the brain is like Velcro for negative experiences and Teflon for positive ones.
So, for starters, be mindful of the degree to which your brain is wired to make you afraid, wired so that you walk around with an ongoing trickle of anxiety to keep you on alert. And wired to zero in on any apparent bad news in a larger stream of information (e.g., fixing on a casual aside from a family member or co-worker), to tune out or de-emphasize reassuring good news, and to keep thinking about the one thing that was negative in a day in which a hundred small things happened, ninety-nine of which were neutral or positive.
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