When you give a reason supporting a claim, see if you can use that same reason as evidence against your claim. For example, if you think aliens probably don't exist because you have never seen any, then can't you say, by the same logic, that the Mashco-Piro tribe probably does not exist? (It does). Seeing this error, you then revise your reason and continue to question each revision in the same way. If the process goes well, you might get to a point where you cannot refute your own argument and are more likely to have a stronger argument than if you did not go through this process. Otherwise, you might realize that your reason for supporting a claim is a poor one and find yourself reevaluating your position on an issue because of critical thought.