Imagine 100 people embarking on a long training program to enter a particular workplace. Now imagine first of all that half of them will never make it.  That’s a 50 percent attrition rate. Out of the half who don’t make it, half of those — 25 percent of the original group — will decide to leave in short order, within one to three years. No problem there: They tried it and decided that it wasn’t for them. But the other half of that group of non-completers — the other 25 percent of the original group — don’t leave right away. They stay many years, twisting in the wind, until they’re finally blown off the tree.