Lightning. Cancer. Heart attack. A drunk driver crossing into your lane. The apparent randomness of this type of event can be horrifying. It's human nature to crave order, answers, explanations, meaning, and purpose for otherwise unanswerable questions. Some people are driven to seek answers; others find their comfort in blissful ignorance. This difference is sometimes termed knowing vs. believing.
So, how is it that we settle our doubts? There are only a few ways by which we come to know and believe, and these were elegantly described in the late 19th century by philosopher C.S. Peirce. He described the four ways that we 'relieve the irritation of doubt' to be via logic ("it is agreeable to reason"), authority ("it was told to me by someone I do not doubt"), tenacity ("I believe it to be so"), and science ("it has been shown to be true"). It is not necessary to make a huge conceptual leap to realize that believing and knowing are significantly different, and the difference is important. As a scientist, I find myself fascinated by the natural world. The laws of nature continually amaze me, and I am in profound awe of how they always work. Sure, I have no way of knowing why those laws exist. The religious amongst us would explain things by pointing to one or more omnipotent gods, but religion is entirely unnecessary. Why the laws of nature came to exist is an unknowable, but on the other hand how the laws of nature function is not only knowable but also important to know.
My religious friends tell me I'm wrong, and often offer evidence or proof that god(s) exist. I mean no offense to the religious -- but they are simply wrongheaded and missing the point. That god(s) exist is an element of faith -- and faith by definition is belief that things are true independent of proof. As soon as one tries to seek proof for such an item, it demeans it and renders it trite. Consider one of the things you believe are true -- a parent's love for a child, for example. Is it necessary for the child to "test" that love or have the parent to "prove" their love? Requiring proof not only demeans the love, but would necessitate that the quantity of love is limited to that amount that can be proven. Thus, if the same reasoning is applied to proving the existence of god(s), then we would inevitable beg the question as god is usually defined as limitless and omnipotent (not to mention omniscient and benevolent).
Why do I get so caught up in knowledge and belief? Simply, because there are vast amounts of pseudo-factual mumbo-jumbo-snake-oil-paramedical-feel-good junk being promulgated as "science". Consider, for example, parents who believe that autism is caused by vaccines. Despite the fact that numerous studies have dismissed any link, some parents are deciding to forgo vaccines and thereby render their children vulnerable to entirely preventable and highly dangerous illnesses. Those parents are quick to point out that autism arises in young children often shortly after being vaccinated, and believe that this correlation of timing is actually evidence of causation. They collapse uncertainty into certainty, ignoring two key facts: nearly every case of autism emerges at about that age, and the incidence of autism is identical in vaccinated and non-vaccinated children. The scientific method requires that a hypothesis be testable, and that once the hypothesis has been disproved it must be discarded. Applied to the hypothesis that "autism is caused by vaccinations", that vaccinated and non-vaccinated children develop the disease at the same rate is enough to disprove it. For some, the belief that autism is caused by vaccines is preferable to the disease being caused by factors they may not be able to explain or control. Their doubt is relieved, and that is soothing, regardless of the implausibility of the explanation. 'Anecdote trumps data' is the lament often uttered by those who try to use rational arguments with those who have made a non-rational decision.
A similar disregard for reason is displayed by those people who believe that climate change is a hoax. The vast quantities of observable data are ignored, even though much of it is obvious even to the non-scientist (for example, shrinking glaciers, ponds that no longer freeze over in winter, numerous heat waves and record high temperatures, 'drunken trees', melting permafrost, etc.). For them, climate change is a hoax perpetuated by scientists trying to get grant money. There is a profound irony in this 'greed and cupidity' explanation in that the groups actively fighting any sort of response to climate change are those that make billions upon billions of dollars from maintaining our addiction to fossil fuels.
In both cases the viewers are blind to the obvious facts, and blame the scientific consensus on a conspiracy. Just as patriotism is the last refuge of scoundrels, conspiracy theories may be the last resort for the uninformed mind. In fairness, perhaps both of the present examples may be better explained by bias. And, the only sure cure for bias is access to truth, ability to reason, and a willingness to change one's mind.