Imagine a world where life expectancy is fixed and the same for everyone at birth, yet people can engage in life expectancy "donation" – meaning that someone can extend your life three years longer at the expense of theirs. Talk about a likely scenario in this world that involves manipulated, coerced donation.
Those with power and money could lure the underprivileged groups into "donating" their life expectancy in exchange for a better future. Assuming that illnesses are still not eradicated, another scenario involving coerced donation could be those in control of the medications force the patients to cut their life short in order to get treated.