Should we opt for the Black Friday discounted price or wait until the   Boxing Day?
  We derive an optimal strategy for minimizing the expected loss in the two-period economy when a pivotal decision needs to be made during the first time period and cannot be subsequently reversed. Our interest in the problem has been motivated by the classical shopper's dilemma during the Black Friday promotion period, and our solution crucially relies on the pioneering work of McDonnell and Abbott on the two-envelope paradox. 
Jiang Wu, Ricardas Zitikis
stat.AP q-fin.TR