The nirvana fallacy is committed when a proposed solution to some problem is rejected because the solution is imperfect, or because it does not adhere to some extreme ideal. This could be because the proposed solution fails to solve the problem completely, would entail certain undesirable consequences, or would be costly or difficult to implement. All of these factors are, of course, relevant considerations when judging a potential course of action, but to argue that a solution should not be implemented simply because some defect can be identified is fallacious, since it is quite possible for an imperfect solution to still be better than no solution, or preferable to any other proposed solution.
The nirvana fallacy is extremely common in political and economic discussions. Almost any proposal concerning social or economic policy is criticised by its opponents on the basis of its flaws, and the various reasons why it will fail to completely solve the problem. Such concerns are relevant, but become fallacious if it is argued that a policy should not be implemented merely because it is imperfect, since it does not follow that an imperfect proposal is necessarily a bad bad. A proposal need only be good enough, represent an improvement, or adhere to preexisting standards for acceptability, in order to be regarded as a good idea.
Safety initiatives are common targets of arguments committing the nirvana fallacy. Examples include:
“I read about a case where a man was thrown from his car wreck and survived only because he wasn’t wearing his seatbelt, so clearly seatbelts aren’t really all that useful for safety.”
“My grandmother smoked a pack of cigarettes a day and she lived to the age of 95, while my non-smoking uncle died at 68, so I don’t think there’s any point in worrying about cutting down on tobacco.”
In both cases, it is being argued that because something (wearing seatbelts, quitting smoking) does not always help, therefore it is never helpful or a waste of time. This is fallacious reasoning since it may still be the case that most of the time seatbelts and quitting smoking safe lives, and therefore on balance both are worth doing, even if they do not guarantee safety and are not perfect solutions.
Nirvana fallacy: overview from Logically Fallacious
Perfect solution fallacy: good introduction from The Skeptic’s Dictionary
Perfect solution fallacy: useful discussion with examples from The Logical Place