The 5 Branches of Philosophy
Life As the Moral Standard
Reason Is Man's Means of Survival
Harmony Of Interests
The virtue of Rationality means the recognition and acceptance of reason as one's only source of knowledge, one's only judge of values and one's only guide to action. ... It means a commitment to the principle that all of one's convictions, values, goals, desires and actions must be based on, derived from, chosen and validated by a process of thought.
Rationality is the habit of acting by reason, which means in accordance with the facts of reality. The only alternative is acting by whim, which because reality is absolute, will result in undesired consequences. This is because an action based on a belief in a particular cause-effect relationship will not occur if that relationship is invalid.
A second consequence to acting irrationally is that it undermines one's ability to act rationally in the future. By choosing to act irrationally, you are confessing your lack of trust in your own mind. The more often you do this, the more you will believe what you are practicing. You will accept that the mind is impotent, and that you cannot make the right decisions. This undercuts your ability to live, since reason is man's means of survival.
Rationality is in your self interest because the only way to achieve desired outcomes is to act according to reality. To understand reality, one must use reason consistently. Any deviation can have long term problems, since one's knowledge is often derived from one's previous knowledge. To accept a false belief once can have the effect of polluting all further knowledge, until the mistakes are cleared away and the new knowledge reevaluated.
Rationality does not mean being a perfectionist in one's thoughts and ideas. It does not require you to spend enormous amounts of time evaluating every idea. It does not require you to learn everything there is to know, to become an expert at every topic. Rationality means acting according to reason. It means accepting only that which you have reason to believe. It means using logic to weed out any contradictions. It means when you have to accept the judgment of another, you use your own mind to determine whether you should. Is the person educated in that field? Is it knowledge that someone is capable of having? From what you know about the rest of his ideas, is he someone you believe will be correct? Rationality is foremost a method of survival. It is a virtue only to the extent that it encourages one's survival.