Pluralistic ignorance
Pluralistic ignorance can be contrasted with the false consensus effect. In pluralistic ignorance, people privately disdain but publicly support a norm (or a belief), while the false consensus effect causes people to wrongly assume that most people think like they do, while in reality most people do not think like they do (and express the disagreement openly). For instance, pluralistic ignorance may lead a student to drink alcohol excessively because she believes that everyone else does that, while in reality everyone else also wishes they could avoid binge drinking, but no one expresses that due to the fear of being ostracized. A false consensus for the same situation would mean that the student believes that most other people do not enjoy excessive drinking, while in fact most other people do enjoy that and openly express their opinion about it.
Rational irrationality
The most famous theory of democratic failure is public choice theory. The theory, developed by James Buchanan, Gordon Tullock, and others, relies on rational ignorance. Voters have a very small probability of influencing policy outcomes, so they do not put much effort to stay up-to-date on politics. This allows special interests to manipulate the political process and engage in rent seeking. A key idea of public choice theory is that many harmful policies have concentrated benefits (experienced by special interests) and diffuse costs. The special interests experiencing the benefits are willing to lobby for the policies, while the costs are spread out very diffusely among a much larger group of people. Because these costs are diffuse, the people bearing the costs do not have enough at stake to lobby against the policies.