8. If the accepted data is changed, all conclusions upon with the data is based must be re-examined.
Most of the tenets of critical thinking are fairly intuitive, part of the common sense that most people already apply to at least some of their thinking. This one, however, is more of a challenge to accept and especially to put into practice. Because data forms the foundation of our worldview, changes to the data can have a devastating effect. I think this is why tend to be so naturally defensive of any piece of data in our minds: we fear for the possibility that contrary data will cause all of our beliefs to be assaulted and come crumbling down around us.
The truth is that this can happen, and it is a good thing. Why go through life with a worldview that is inaccurate because of fear? The whole purpose of a worldview is to help us understand the world. If it is not accurate, then our understand of the world suffers, and we are less likely to achieve our goals and ultimately achieve happiness.
For example: let's say you wish to avoid caffeine. In order to do so, you avoid dark colored sodas (Coke, Pepsi, Dr. Pepper), which you believe to contain caffeine, and drink only light-colored ones (Sprite, 7-Up, Orange Crush), which you believe to be caffeine-free. Later you may encounter some data which proves this generalization cannot be counted on, for example, Mountain Dew which contains caffeine but is clear, and most root beer which is dark but is caffeine-free. At this point you should throw out the data which told you that the darkness of a always relates to its caffeine content.
Surprisingly enough, many people may be unwilling to abandon a belief like this, even when shown hard data which refutes their belief (say, the list of ingrediants on the soda can). It's hard for people to let go of their worldview; to admit that they were wrong. I think this is because it makes us aware of our failability, just how little we know (and can know) about this big, complicated world. And that makes us feel powerless, which is scary.
Here's a heavier example which illustrates why people are hard-pressed to relinquish even obviously wrong data and conclusions. Imagine someone named Kim, who as a young adult becomes aware of a number of new studies which show the health benefits of a particular vitamin. She becomes involved with an advocacy group that lobbies food and food supplement producers to include more of this vitamin; to educate children and adults about its benefits; and to research ways to synthesize or extract the vitamin so that it can be more affordable to the poor. She spends ten years trumpeting the value of the vitamin. She rises through the ranks and eventually is made president of the organization. She is doing good work, is paid well, and feels good about herself.
Then some new studies are undertaken, attempting to re-create the results of the original studies. These new studies find that, in fact, the vitamin is not nearly as important to health as was previously thought. The early studies made a mistake in their control groups, and the group that was tested with the vitamin had significantly healthy diets in other ways.
What should Kim's course of action be at this point? If she is a critical thinker, she will be extremely interesting in this new information. She should look over all the information for all of the studies, trying to understand it as well as she can. Given her role in the advocacy group, it might even be reasonable for her to contact some of the researches and interview them, to get a better grasp of the results, and perhaps even suggest other possibilities that they might explore. She should allocate funds from her organization to launching another study, making every effort to make sure that the scientists involved are qualified, thorough, and impartial. She will tell them that the most important thing is that they find the truth, not that they come up with a result that agrees with the mission of her organization.
She should do all this because the answer is extremely relevant to her organization and her own career. If the answer is that the vitamin isn't particularly beneficial, she and all the organization's supporters will want to know this so that they can cut their losses, and move onto something more productive. If the answer is that the vitamin is beneficial as was previously though, she and the entire organization can sleep better at night knowing that their claims had been submitted to the toughest, most rigorous examination possible, and have passed with flying colors.
But that's probably not what she will do. After all, she's got a nice, cushy job; she's invested many years of her life; the investors don't want to hear that they've put millions of dollars into promoting something that turns out to be worthless. The anguish of realizing that it was all for naught is more than most people can bear. So, amazingly, they just stick with it - continuing right on with what they were doing before, even though the evidence that it is a waste of time is as clear as day.
To be a critical thinker, you must internalize the following:
These points are a lot harder to enact than they sound. But this is the beginning of true wisdom. Say these aloud to yourself. Believe them. And next time someone confronts you with some contrary data, pause and take a deep breath. Repeat to yourself, "I can be wrong." Then listen to what they have to say, see if it should make you question your beliefs. And then, it probably won't - because if you know you can be wrong, then your beliefs are likely to be solid. And then you can say to yourself, "I can be wrong, but I'm not in this case. Take that, world!"