EVERYONE knows the power of deadlines  and we all hate them. But their effectiveness is undeniable. People procrastinate. Deadlines help. They speed up performance and, paradoxically, reduce the anxiety of uncertainty. So when President Obama announced on Tuesday night a strict timetable of 18 months before the drawdown of troops from Afghanistan  how did that affect the psychology of the nation?

The emotional effect of the pronouncement depends on the party involved. For the military brass, 18 months is a blink of an eye, so the deadline could motivate them to perform at their peak, or it might paralyze them with fear; for the troops and their loved ones, 18 months is an eternity. But for all those with an immediate stake in the war, a clear timetable reduces uncertainty  at least along the “when” dimension, if not the “what” dimension.

After all, no one likes to wait. And the only thing worse than waiting is waiting with uncertainty. A team at Emory University examined what happened when people waited for an impending electrical shock. Some people dreaded the shock so deeply that they chose to receive a more powerful shock earlier rather than wait for a lesser shock to arrive at a later, random time.

One of the key jobs of the human brain is to simulate the future, and the less information it has to work with, the more anxious it becomes. Pinning things down in time makes waiting less troubling. With a clear idea about the order and timescale of events, people are more patient and less anxious. And that is the hope implicit in President Obama’s declaration of a timeline.