Unless victims of violence, disease, or accident, an elf could once expect to live for over three thousand years, untouched by the ravages of time. While their flesh was notably timeless, however, their minds were not. Elven awareness could withstand only so much memory, and the inexorable progress of time created a phenomenon known as "drift" among their elders.
Drift occurs when an elf begins to lose his past. The nightly memory-meditations prove incapable of preserving the vast stretch of time behind him, and gradually details and whole events are lost to forgetfulness. An archmage who begins to study glassworking in order to create a magnificent planar astrolabe might end up spending so much time on the study that he begins to forget the original purpose of the learning. Even a master swordsage who strives desperately to hold together his recollections will eventually neglect some crucial memory only to find that it was the lynchpin of his past, recollections tumbling into the void despite his efforts to save them. The more heroic and elaborate his mastery, the more he has to maintain in order to keep it.
Even when reminded of lost memories, the reminders have no force- his recollections have simply been lost under the accumulated drift of years and mouldered with neglect. Within days, the archmage is simply a glassblower, perfectly content in his trade and aware of his past only through mouldering notes and books he no longer remembers how to read. The swordsage finds himself incapable of the simplest maneuvers, and might even have forgotten he was a swordsman at all.
This effect has changed with the appearance of the Immanent and the True. The Immanent are no longer subject to Drift of any kind. While they are born, live, and die in no more than three centuries, their memories are no more fragile or transient than those of men or dwarves. Drift has ceased to exist for these elves. For the True, Drift has become even more crushingly final. When a True Drifts, it is not simply that they forget, but that they become a completely different being, with a completely different past remembered. A kind and benevolent male True might rise from his trance as a female True of brutal temper, one with a completely different memory of the past that rarely has any correspondence with the truth.
Drift is a form of death to the elves. They are aware that the person they used to be simply no longer exists as such. The combination of memory and experience that formed them is lost to time, and what they are now no longer shares even a body with what they once were. They are someone else entirely, and the former identity is lost forever.
Formerly, Drift rarely occurred among young elves. Only those who have at least four or five centuries of life behind them were apt to lose their past. The more focused and determined elves could maintain more of their past, depending on how complex it was, but this tendency to Drift was a major reason why there were not a great profusion of elven heroes who wielded the experience of centuries. Stories were told of Drifted elves who suddenly recollected their past as mighty swordsages and arcane lords, but most discount them as mere wishful thinking. Among the True these days, Drift is an even more final termination of existence.