Unbelief is the opposite of belief. Unbelief is to refuse to believe something even when given sufficient reasons to.
As humans, we are constantly working against strong psychological and cognitive biases that prevent us from considering new ideas, especially those that contradict things we hold as important.
A prerequisite for belief is a willingness to consider beliefs other than those you already believe:
...even if ye can no more than desire to believe, let this desire work in you, even until ye believe in a manner that ye can give place for a portion of my words. (Alma 32:27)
While this seems obvious, it is a big problem.
In modern times, there is an all-out assault on both religious and secular belief. We are paradoxically told that long-standing historical beliefs are false and were always so, in spite of objective positive outcomes, while we are simultaneously told that modern, extreme deviations from these beliefs are true, have always been true, and will always be true, in spite of any supporting evidence to that end.
One of these new beliefs is that we are all the same—that any objective differences we see are either figments of the imagination or the vestigial effect of past injustice, and that no one should think or act differently than how they are told.
Belief, whether in the form of desires, reasons, or actions, will always differentiate people, because people will always choose to have different desires, find and accept different reasons, and take different actions.
Those who desire more than others will always live a different life than those who are satisfied with a lesser life. Those who reason more effectively than others will always develop more wisdom and knowledge than those who reason less effectively. Those who act more than others will always achieve more than those who are idle. The products of these practices are outcomes, and those who exceed their peers in one or more aspects of faith will always obtain outcomes beyond those who do not.
Don’t disbelieve anything you have been given sufficient reason to believe. Don’t believe anything you haven’t been given sufficient reason to believe at the cost of anything you have. Don’t buy into the lie that beliefs don’t matter. Ideas do, in fact, have consequences—massive consequences that extend through every outcome in life and in eternity.
Faithful steps tend to build on each other, magnifying the differences in outcomes between those who rightly wrangle with them and those who do not. Those who are willing to open-mindedly consider new information and walk in uncertain paths when given sufficient reason to will have much more abundant lives than those who are not.