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.
Stupidity
In "Understanding Stupidity", James F. Welles defines stupidity this way: "The term may be used to designate a mentality which is considered to be informed, deliberate and maladaptive." Welles distinguishes stupidity from ignorance; one must know they are acting in their own worst interest. Secondly, it must be a choice, not a forced act or accident. Lastly, it requires the activity to be maladaptive, in that it is in the worst interest of the actor, and specifically done to prevent adaption to new data or existing circumstances."