310 M. Hoffman et al. Norms. People are typically conditionally cooperative, meaning that they are will- ing to cooperate more when they believe others contribute more. For example, stu- dents asked to donate to a university charity gave 2.3 percentage points more when told that others had given at a rate of 64 % than when they were told giving rates were 46 % (Frey & Meier, 2004). Hotel patrons were 26 % more likely to reuse their towels when informed most others had done the same (Goldstein, Cialdini, & Griskevicius, 2008). Households have been shown to meaningfully reduce electric- ity consumption when told neighbors are consuming less, both in the United States (Ayres, Raseman, & Shih, 2012) and in India (Sudarshan, 2014). Such conditional cooperation is easily explained by the game theory model: When others give, one can infer that one is expected to give and may be socially sanctioned if one does not. Strategic Ignorance. Those at high risk of contracting a sexually transmitted dis- ease (STD) often go untested, presumably because if they knew they had the STD, they would feel morally obliged to refrain from otherwise desirable activity that risks spreading the STD. Why is it more reproachable to knowingly put a sexual partner at risk when one knows one has the STD than to knowingly put a sexual partner at risk by not getting tested? There is evidence that we sometimes pursue strategic ignorance and avoid information about the negative consequences of our decisions to others. When subjects are shown two options, one that is better for themselves but worse for their partners and one that is worse for themselves but bet- ter for their partners, many choose the option that is better for their partners. But, when subjects must first press a button (at no cost) to reveal which option is better for their partners, they choose to remain ignorant and simply select the option that is best for themselves (Dana, Weber, & Kuang, 2007). This quirk of our moral system is