Why do we believe any given proposition? To my mind, there are two valid reasons for belief in any proposition. First, your belief may be logically derived from a set of axioms and other derived true propositions. Not many beliefs fall into this category because truly axiomatic propositions are not in great supply.
So what is the other valid reason for believing in a particular proposition? In my opinion, it is also valid to believe in a proposition if the balance of evidence shows it to be likely to be true. For many propositions, it is appropriate to consider both the truth and falsehood of any particular proposition according to the likelihood that each is the correct value of the proposition. For other propositions, the nature of the evidence is such that it is not worth the effort to consider the likelihood that it is false because this possibility is infinitesimal. Whether or not one should factor the likelihood of a proposition's truth value into any decision is directly related to the costs and benefits of the possible consequences of the decision.
However, even when it is highly likely that a proposition is true because of the nature of the evidence for it, you must go one step further if you desire to be truly veracious. You must be able to identify those conditions that are sufficient to disprove the proposition you believe. You must show how the proposition is falsifiable.
If you cannot identify these conditions, then you do not have a reason for believing in that proposition. You must admit to yourself that the evidence that you are using to support your proposition is simply confirming a preexisting bias because no evidence would convince you to change your mind.
Indeed, the ideal is to identify the full set of conditions that falsify the proposition. It is quite easy to identify a highly improbable criterion to falsify a proposition. We should not take satisfaction in this. If there are other falsifying conditions, we need to identify them too. Otherwise, we will build a disingenuous shield around our cherished biases by finding only ridiculous falsifying conditions. This will give us the misguided self-satisfaction of believing that we are intellectually honest while stacking the deck in favor of not rejecting the beliefs we cherish.
Identifying a set of falsifying conditions is not easy. Indeed, it is likely that we will never fully identify the set of falsifying conditions for any particular proposition. Nonetheless, by seeking to know those conditions that will cause us to validly reject the things we now wrongly believe, we maximize the likelihood that what we believe will be true. That is the best we can do.