Rationality is a ritual, one that involves light, vague estimates of costs and benefits
They're so light, that one wonders if they can even be called rational. For example, when you ask for help and someone volunteers it, neither party is really measuring cost-benefit because the stakes are so low. Rather, all our actions are just a matter of drives and culture. Likewise, in the case of voting, it's not a rational decision for most of the electorate.