Suppose you will soon be subject to torture and degradation, such that you would prefer to die beforehand. Suicide is not allowed, but you are offered the opportunity to have all traces of your psychological self purged from your brain -- memories, character, talents, etc. Would that help? Would you fear the upcoming torture any less, perhaps believing that it would now be someone else rather than you who endures it?
How about if your psychological traces are completely transferred into the brain of another person, who goes on to live a happy, torture-free life?
Suppose now that the psychological transfer is compulsory, but beforehand you get to choose which body will be subsequently tortured. What would you choose?
(Cases from Bernard Williams, 'The Self and the Future'.)