I believe uncertainty is what empowered every major change in human history that dealt with revolution of some sort - both good and bad. “I'm not sure about . . .” is the starting point for all kinds of ennobling and enabling movements. The only problem, in my opinion, is when “I'm not sure if . . . ” leads to “I doubt that . . . therefore, I can’t . . . until I no longer doubt.”
1) “Faith” is not “knowledge”. It is the substance of things “hoped for” - the evidence of things “not seen”. Faith is based on “hope” - a desire for something that cannot be seen or understood fully. “Certainty” is the end of faith - the desired outcome. It is to be sure of something to such a degree that it is expressed most often in terms of knowledge. “I know this” and “I am certain of this” are seen generally as saying the same thing.
2) On the other hand, “doubt” is not a lack of certainty. It is not a passive lack of belief or faith, but rather an active disbelief. It is expressed as a negative. It is NOT expressed as, “I am not certain of that,” but rather as, “I doubt that is true” - meaning, “I don’t think that is true,” or “I don’t believe that is true.”
3) Faith exists NOT in conjunction with doubt, but rather it functions side-by-side with “uncertainty”. One exercises faith when one is uncertain; one does NOT exercise faith when one doubts. When one doubts s/he actively disbelieves - thus, the one who said he would not believe until he personally had seen and touched was called “Doubting Thomas”. He didn’t say, “I’m not sure.” He said, instead, “I will not believe unless . . .” He could not exercise faith, not because he was uncertain, but rather because he actively doubted.
I get more than a little bit frustrated by the insistence that everyone can know everything, but I have no issue with the idea that faith and doubt cannot co-exist. Faith is the active expression of an internal orientation toward belief; doubt is the active expression of an internal orientation toward disbelief. Therefore, based on a strict parsing of the technical meaning, they can’t co-exist - since they are opposites. However, because we tend to conflate and confuse doubt and uncertainty, I do have an issue with the idea that faith and doubt cannot co-exist IF what the people who say that really mean is that faith and uncertainty cannot co-exist - that if I am uncertain of something, then I lack faith. That is a fundamental misunderstanding of faith.
I would posit that we all must, by definition, exercise faith until we are certain - and then hold onto that previous faith again if we lose certainty. Since none of us can be certain about everything imaginable, every one of us needs faith in something all our lives. If we are certain of everything, I believe we either are ignorant or delusional. What we cannot do, however, is cultivate a doubting spirit. If we never reach an acceptable level of certainty, then we need to accept a life of searching - following whatever principles and people and politics and religion we feel provide us with the highest degree of certainty we can obtain. What we have to avoid is becoming our own version of Doubting Thomas.
Finally, we are told that Jesus experienced everything we possibly can experience - including the crushing weight of being judged to be guilty. That must include doubt (or something similar enough to qualify) if it is to be comprehensive. Generally, we do not associate "doubt" with the Savior and Redeemer of the world (God, the Son) - but, again, doubt means not wanting to believe or accept something. However, there were at least two times when I think it is safe to say that He struggled mightily - because He didn’t understand and didn't want to accept something. (In the Garden, where He asked if the cup could be taken from Him and on the cross when he cried out and asked why His Father had forsaken Him.) In these cases, he seems to have been uncertain about some aspect of the Atonement and, possibly, even doubted temporarily: specifically, if He would be able to do it and then why He had to do it alone at the very end. I hesitate to call those "doubts" - but it might be a fair assessment. I prefer to call it "enduring uncertainty".