In fact, most of the time, we are experts in fallibility. Too often for our satisfaction, readers confront us with fascinating Imponderables that we cannot answer. These Imponderables tend to fall into two groups: mysteries that totally baffle the experts we consult; or mysteries that every expert has an opinion on, but for which there is no consensus. Either way, our inability to answer these questions makes us frustrated. So, we throw Frustables (short for “frustrating Imponderables”) out to you in the fervent hope that you can do better than we can. It’s amazing how often you can, as demonstrated in the Frustables Update section that follows. To lure you into sharing your wisdom, we offer a complimentary, autographed copy of our next volume of Imponderables to the first person who can lead to the proof that solves any of these Frustables. And of course, your contribution will be displayed and acknowledged in the book. But don’t get smug until you see the new Frustables. Solving these will not be easy.