The interest is very low, since it’s guaranteed by assets. The cost of the interest is less than taxes. So, as soon as one loan expires you take out another. You keep taking them out until you die, then your estate pays the loans back out of the estate and then the rest passes on to your offspring. If you want to know more, there isn’t more to know really but you can Google it. This buy-borrow-die scheme wasn’t made public until the last few years and details are still scant.