My occasionally referred to favorite teacher Moshe Caspi devised a very simple, and probably rather frivolous, measure for attention span: age times 2, but never more than 20 minutes. Regardless of whether there's really any scientific basis for this claim, the basic idea is pretty simple: even when we work very hard at it, our concentration span just ain't very long. Perhaps when we do succeed in devoting our undivided attention to something it's only because we haven't noticed the short breaks that we've allowed ourselves, or because we've noticed them, and accepted them. Perhaps we get work done precisely because we jump from topic to topic and permit our minds to wander, thus keeping these breaks under control. If we didn't allow this jumping and wandering our minds would be doing it on their own, and the consequences might be much more serious than they actually are.