Most of us know that eyewitness testimony is often inaccurate. But what about our own memories? Especially our recollections of emotionally charged events—so-called “flashbulb memories”? We’re pretty sure that they’re vividly accurate, even when they aren’t.

Why that is is just one of a complex of psychological phenomena Tali Sharot explores in her illuminating and vastly entertaining first book, The Optimism Bias. Sharot, a researcher in neuropsychology at the Wellcome Trust Center for Neuroimaging at University College London, makes two major claims here: Most of us are optimistic, and we are optimistic because our brains have evolved to make us so. Why? Because the optimistic belief that we are all slightly better than the average “makes health and progress more likely,” and that set of mild illusions has helped humans to survive and progress. “Optimism,” Sharot writes, “may be so essential to our survival that it is hardwired into our most complex organ, the brain.”

Such observations could smack of psychobabble, except for the fact that Sharot and colleagues have produced fascinating brain imaging experiments and data that support her assertions. You can’t read this book and disagree that, as Sharot writes, “the human brain . . . is extremely efficient at turning lead into gold.”

Sharot subtitles her book “A Tour of the Irrationally Positive Brain.” “Tour” is a good description, as she explores facets of our ability to delude ourselves, taking us on a magical mystery tour of our perceptions, rather than making a step-by-step argument. “Tour” also evokes the pleasure Sharot gives us in her surprising, research-based observations (“Political stability is one of the nine strongest indicators of a nation’s well-being, and human rights is one of the two strongest.”), her use of contemporary examples (“from the dark skies of Sham el-Sheikh to the crowded lockers of the Los Angeles Lakers”) and her pleasing sense of humor (discussing experiments with mice, for example, she acknowledges that humans are quite different but notes “like humans, however, these mammals are frequently found in the kitchen in the middle of the night, searching for leftovers”).

Sharot also acknowledges that optimism, at least extreme optimism, has its downside—sometimes leading to risky, life-threatening behavior. So while she doesn’t directly say it, her book certainly suggests that we need a little humility to accompany our certainties. A little—but not too much.

As the actor Carleton Young declared in The Man Who Shot Liberty Valence, “When the legend becomes fact, print the legend.” That’s exactly what happened in the April 1913 issue of National Geographic, when the entire magazine was devoted to explorer Hiram Bingham III’s “discovery” of ancient Inca ruins in Peru. In his meticulously researched and marvelously readable book Turn Right at Machu Picchu, author and adventurer Mark Adams retraces the steps that led Bingham to the famed site 100 years ago this July.

Adams, whose Mr. America was named a Best Book of 2009 by the Washington Post, goes beyond merely printing the legend: He studies it, he lives it . . . and he debunks it. At first glance, it seems like Adams might have been following in the footsteps of Bill Bryson’s A Walk in the Woods, given the book’s “maybe-I-should-have-worked-out-just-a-little-bit-more-before-starting-this-physically-demanding-quest” setting. Like Bryson, Adams peppers his book with interesting anecdotes, trenchant observations and frequently hilarious asides. But as the chapters (which more or less alternate between Bingham’s and Adams’ expeditions) fly by, both the book’s scholarship and its organization also call to mind John McPhee’s excellent history/travelogue of Alaska, Coming into the Country.

Even if you’ve never traveled farther than the Jungle Cruise at Walt Disney World, you’re guaranteed to be swept up in Adams’ vivid descriptions of the near-unpronounceable sights along the Inca trail, as well as the remarkable amount of information he tactfully packs into a single paragraph:

“We walked down the mountainside beneath Llactapata and crossed the Aobamba River—an important milestone, because we were now officially inside the Machu Picchu Historical Sanctuary. Technically, this zone is a haven not only for ruins but for the diverse flora and fauna of the region. (This is one of the few safe places for the rare Andean spectacled bear, which looks like a cross between a raccoon and a black bear cub.) There is one important eco-exception—the gigantic hydroelectrical plant on the backside of Machu Picchu. John and I walked past dozens of men in matching hard hats and coveralls driving heavy machinery; a funicular ran up the mountainside. KEEP OUT signs were posted everywhere. None of this is visible from the sacred ruins directly above. It was like stumbling upon a Bond villain’s secret hideout while hiking in Yosemite.”

Perhaps, in the best-case scenario, Adams’ book might impel you to adopt the motto of one of his former employers, Adventure magazine: “Dream it. Plan it. Do it.” And at the very least, you’ll get an unparalleled insight into how demanding, and how rewarding, following that dictum can be.