The Lindy effect is an idea that the future life expectancy of some non-perishable things like a technology or an idea is proportional to their current age, so that every additional period of survival implies a longer remaining life expectancy. Where the Lindy effect applies, mortality rate decreases with time. In contrast, living creatures and mechanical things follow a bathtub curve where, after "childhood", the mortality rate increases with time. Because life expectancy is probabilistically derived, a thing may become extinct before its "expected" survival. In other words, one needs to gauge both the age and "health" of the thing to determine continued survival.
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Origin
The origin of the term and idea can be traced to Albert Goldman and a 1964 article he had written in The New Republic titled "Lindy's Law'. In it he stated that "the future career expectations of a television comedian is proportional to the total amount of his past exposure on the medium". The term Lindy refers to the NY Deli Lindy's where comedians "foregather every night at Lindy's, where... they conduct post-mortems on recent show biz "action". Benoit Mandelbrot formally coined the term Lindy Effect in his 1984 Book The Fractal Geometry of Nature. Mandelbrot expressed mathematically that for certain things bounded by the life of the producer, like human promise, future life expectancy is proportional to the past. He references Lindy's Law and a parable of the young poets’ cemetery and then applies to researchers and their publications: "However long a person's past collected works, it will on the average continue for an equal additional amount. When it eventually stops, it breaks off at precisely half of its promise."
Nassim Taleb furthered the idea in the The Black Swan: The Impact of the Highly Improbable by extending to a certain class of nonperishables where life expectancy can be expressed as power laws.
With human projects and ventures we have another story. These are often scalable, as I said in Chapter 3. With scalable variables… you will witness the exact opposite effect. Let's say a project is expected to terminate in 79 days, the same expectation in days as the newborn female has in years. On the 79th day, if the project is not finished, it will be expected to take another 25 days to complete. But on the 90th day, if the project is still not completed, it should have about 58 days to go. On the 100th, it should have 89 days to go. On the 119th, it should have an extra 149 days. On day 600, if the project is not done, you will be expected to need an extra 1,590 days. As you see, the longer you wait, the longer you will be expected to wait
In Taleb's book Antifragile: Things That Gain from Disorder he for the first time explicitly referred to his idea as the Lindy Effect, removed the bounds of the life of the producer to include anything that doesn't have a natural upper bound and incorporated it into his broader theory of the Antifragile.
If a book has been in print for forty years, I can expect it to be in print for another forty years. But, and that is the main difference, if it survives another decade, then it will be expected to be in print another fifty years. This, simply, as a rule, tells you why things that have been around for a long time are not "aging" like persons, but "aging" in reverse. Every year that passes without extinction doubles the additional life expectancy. This is an indicator of some robustness. The robustness of an item is proportional to its life!
Mandelbrot agreed with Taleb's expanded definition of the Lindy Effect: "[Taleb] suggested the boundary perishable/nonperishable and he [Mandelbrot] agreed that the nonperishable would be powerlaw distributed while the perishable (the initial Lindy story) worked as a mere metaphor."
The Lindy effect is a more general form of the later Copernican principle, in the sense of the generalized Doomsday argument by J. Richard Gott. This states that the future life expectancy is equal to the current age, not simply proportional, and is based on a simpler argument that, barring additional evidence, something is halfway through its life span.
Usage
The Lindy Effect "... allows us to figure out how time and things work without quite getting inside the complexity of time's mind. Time is scientifically equivalent to disorder, and things that gain from disorder are what this author [Taleb] calls 'antifragile.'" So things that have been in existence for a long period of time can be considered more robust/antifragile (i.e., more likely to continue to survive) than new things that haven't passed the test of time. Given this, the Lindy Effect can be used to distinguish random survivors from non-random survivors and gauge the fragility of a thing which provides information that can help with decision making. For example, companies that have been around the longest and are still relatively "healthy" will last the longest, and vice versa. Investors can use the Lindy effect to narrow down their choice of stocks to the most durable companies.
Pareto distribution
Lifetimes following the Pareto distribution (a power-law distribution) demonstrate the Lindy effect. For example with the parameter
More generally with proportionality rather than equality, given