Rationality is defined as “…the quality or state of being rational – that is, being based on or agreeable to reason. Rationality implies the conformity of one’s beliefs with one’s reasons to believe, and of one’s actions with one’s reasons for action…When the goal or problem involves making a decision, rationality factors in all information that is available (e.g. complete or incomplete knowledge). Collectively, the formulation and background assumptions are the models within which rationality applies. Rationality is relative: if one accepts a model in which benefitting oneself is optimal, then rationality is equated with behavior that is self-interested to the point of being selfish; whereas if one accepts a model in which benefiting the group is optimal, then purely selfish behavior is deemed irrational. It is thus meaningless to assert rationality without also specifying the background model assumptions describing how the problem is framed and formulated.”
The salient point here is to have as much knowledge as possible to make the optimal choice. Complete understanding entails knowing what is true, but also what is false. Even if the truth is unknowable or beyond one’s grasp, errors in reasoning can still be identified, as the examples below show:
You are feeling career envy, watching people who you knew suddenly become much more successful than you. Or you read stories of successful people, and think that their lives must be superior and more enriching compared to your own life. Someone gives advice or attempts rationalize this by arguing that such people may also have misfortune and pain in their lives and that the outward appearance of being successful and happy masks possible hardship. Why is this logic fallacious? Because these are mutually exclusive outcomes. A grave personal misfortune, such as a family member dying of cancer, is statistically independent of one’s professional success; being successful does not up the odds of a family member having cancer, divorce, your home burning down, or whatever.
Example 2: You want to rank your YouTube videos higher for your company, so you hire a consultant to try to determine what factors are involved in YouTube rankings. He says that videos that rank well have a hundreds or even thousands of comments, implying that you should pay people to post comments on your videos. Explain why this is possibly fallacious. Because correlation does not equal causation. Such videos have a lot of comments because they are popular due to ranking well and other factors; the comments don’t lead to the popularity and rankings.
Example 3: Someone argues that women are smarter and or more industrious than men because women have a higher college graduation rate than men. Why can we not conclude this? Because it’s also possible that women are majoring in easier subjects. Assuming that college completion rates are predictive of IQ, it would also be useful to break it down by subject, such as male vs. female STEM graduation rates, and then even by GPA, too. Even if you don’t know the the actual data about GPAs, the logical errors are glaring enough that we cannot take the premise as true.