How could he forget?

In a study done at Tohoku University in Sendai, Japan, and published in February, a psychologist had 19 men and women keep diaries over two weeks, recording lapses in memory and judgment as well as their moods at the time of the mistakes. Lapses were most common when the men and women were highly preoccupied with some project or problem. "Especially when people are doing something absolutely engrossing, something they love, they can get carried away for long periods of time," said Braver.

The state of almost meditative concentration is similar to what the Hungarian-born psychologist Mihaly Csikszentmihalyi, a leading researcher in the field of creativity, calls "flow." A widely recognized psychological state, flow is the total absorption that occurs when people are involved in an activity for its own sake, using their skills to solve a puzzle, complete a job or play a game, whether tennis or chess. It's the equivalent of an athlete being "in the zone," a jazz player losing himself in a melody or a computer science professor working out an especially challenging problem. During "flow" moments, one's ego and sense of time are set aside.

It is, in short, a wonderful state of consciousness -- unless you've left a child in the car.

There's no foolproof method for avoiding lapses altogether; we are all human, each with our own absent-minded routines, our engrossing hobbies or work. But psychologists say it does pay to be aware how flawed memory is, and how it usually goes wrong for ourselves, personally. Some people simply cannot hold more than a couple of thoughts in working memory at a time; others are prone to absent-minded routine; and still others are extremely tuned in -- usually.

"No matter how good your internal alarm, you can't expect it to work every minute of every day for every person," said Schacter. "The sad lesson we learn from these tragic deaths is that when it comes to memory, you can't assume it won't betray you."