The Demonstration is based on a two-step model in which some policyholders die during the first period and the remaining policyholders either lapse or live for some time thereafter. The expected life span varies depending on whether the policyholder lapses or not: in the real world, lapsing policyholders tend to have longer expected life spans than non-lapsing policyholders.
Mathematica computes the premium needed to break even based on the user's choices as to the lapse rate, the fraction of the reserve paid to lapsing policyholders, the percentage of policyholders dying during the first period, the expected life span of lapsers and non-lapsers, the interest (discount) rate, and the overhead of running the insurance system as a percentage of premium. The Demonstration calculates the level premium needed for the insurer to break even, the size of the reserve at the time living policyholders have the option to lapse, the payout upon lapse, and the return a spin investor could expect to see, i.e., someone purchasing a policy during the first period knowing for sure that, so long as the insured survived, they would not lapse.
When there is no life expectancy differential among lapsers and non-lapsers, spin life fails to make money. Lower payments on lapses coupled with lower overhead can result in low premiums and make spin life very profitable.