For me, truth is a matter of the imagination, as Ursula Le Guin said, or rather as she imagined Genly Ai telling her that. (See the ~ 1976 Introduction to the rerelease of the 1969 award winning science fiction novel, THE LEFT HAND OF DARKNESS.)
Truth is not the imagination, but the presence of truth always includes the imagination. In LDS scripture, we learn that truth is what happened, what's happening, what will happen. I know (or I imagine) that when I consider what happened, I use my imagination. I doubt that any person is and different than me in that regard. When I consider what will happen, I also use my imagination. I hesitate to think anyone else doesn't do that, too, although, perhaps, I could imagine it. When I consider what is happening, like me typing this out right now, trying to make sense, to select a rational order of words, etc., there is no doubt that I call on my imagination to deliver it contemporaneously.
"What if" is an element of the imagination; it is a feature of existence. It is not ever-present; it comes and goes. We don't like it continually present and work to eliminate it.
Fear is at the core of our being; essential to our very survival. It is also at the core of religion, of the LDS canon, and of other doctrines far and wide. It is a catalyst to action and to analysis and change. We use our imaginations to deal with fear.
Was that the sound of the cat knocking the toaster off the counter, a shutter bumping in the breeze, or a prowler? If the sound is fearful enough, we respond automatically --- fight or flight kicks in --- without analysis. Examination of what happened then comes later, and we use our imaginations to relive and evaluate the experience, to make changes, adaptations, etc. for good or for bad.
There is a time and a place to doubt just as there is a time to eat and sleep.