[bscphil]

Right, correcting for survivorship bias is very important. If an object lasts one year, its expected life isn't now $average_use_life - 1; that's too low an estimate.

The problem with the "half life" rule is that it corrects for this in the dumbest possible way, not only providing an inaccurate estimate for most of the object's life, but even getting the first derivative wrong for most objects. Usually, lasting longer does not make the expected remaining years of service go up, but the rule implies it does!

Take people for example. At birth, a woman in the United States has a life expectancy of 81. If she makes it to 60, she can now expect to make it to ... 85. Not a big change! Every year she lived (even her first), her remaining life expectancy went down, not up. See this chart I made comparing the life expectancy of people versus a theoretical "half-lifer": https://0x0.st/otZ_.png