Unfortunately, people who cannot tell contrary truths usually wind up lying in the end. That is because most truths consist of contradiction. Minus the ability to say “on the one hand” and match it with “on the other,” our most strident positions amount to holding one hand behind our backs, fingers crossed as our noses grow longer. We would have better conversations and more meaningful debates if we held out both our hands. The rift over Gaza now threatening to divide the Democratic Party and ease Donald Trump’s return to the White House is largely rooted in an inability to...