Even the most meticulously managed PDA won't work if you misplace it. And as luck would have it, the items we lose most often—keys, glasses, wallets, cell phones, planners—are the ones that are crucial to our survival.

This abject failure to keep track of our belongings may emerge from the brain's talent for forecasting the future. The neocortex, a long-term storage facility, constantly predicts how we'll behave in specific situations, explains Jeff Hawkins in his book On Intelligence. Instead of reinventing the wheel every time we do something familiar, the brain chooses from a library of existing patterns, based on choices we've made before. A novel event—a man with a gun—gets the brain's full attention, but when we're merely lugging groceries into the house, we shift into autopilot. And autopilot is the mode in which we're likely to misplace things.

The problem can be remedied, but only with a preemptive strike. Awareness is essential: When the phone rings as you're entering the house loaded down with groceries, don't drop your keys on the counter, where they will be buried in the day's mail, making you frantically late for your dinner engagement. If you can't immediately hang the keys on the hook where they belong, keep them on your person until you can; one woman I know slips them into her bra, creating a silhouette so inelegant that she can't possibly forget where she put them. Give up your habit of tucking important items into indiscriminate pockets of your purse or briefcase. Choose one secure zone—front, zippered—where you always keep your boarding pass or passport, and never alter it. You'll save yourself the discomfort of searching high and low under the stern surveillance of security personnel.