I wouldn't go so far as to call it a need, but uncertainty definitely bothers me because it makes life a lot more complicated and messy. I've had to learn to live with it, because I can't logically avoid it. I hated the idea when I first heard about it at school - they had a lesson in which they showed us that questions don't always have clear-cut answers.
Later on in science we heard about the inevitable error in quantifying things, and how standard deviations could be used to quantify the error itself. I think it's very clever how that can be done, moving the data on from "we can't be certain it's exactly correct" to "we are 99% certain that the result lies between x and y." I didn't like it, but it was at least a coping strategy.
I read in a book that "we live in the assumptive world," i.e. we tend to act and think as though we are certain of things that we're not completely certain about. I didn't like that either, but often it's the only way to get anything done. I remember being very literal at work, and when a scientist (verbally) jumped to a conclusion, I thought he'd lost the plot, but he hadn't. He knew he could be wrong, but like most people he simplified what he said, and didn't want to get too long-winded by preceding his every suggestion by "it appears reasonably safe to assume that...." Of course if he'd been writing a scientific paper, he'd have been much more accurate. Interestingly, he was the guy who told me once, when I was being rather risk-averse and slow, "I think we can afford to proceed with more confidence." That's a concept I like to include whenever I catch myself being extremely careful.
Interestingly, it's this stickling for accuracy that lengthens a lot of the things I say, as if I'm afraid of saying anything that isn't absolutely certain and correct. I still have a hard time getting it through my head that nobody is completely innocent of talking complete rubbish.
I've come to be very suspicious of certainty in others, especially in leaders. One particularly nasty form of this is "moral certainty." Ideas about material things can often be fairly accurate, sometimes astonishingly so, but ethics is a very messy subject.
As for faith, the only kind of faith I can understand or do is the kind where a person doesn't know a thing is true for sure but behaves as though it's correct. Best example I know is the New Testament story about somebody lowering a sick man through the roof of a house because it was the only way to get a healer to notice him. The New Testament calls that faith and (if I remember right) says it was the reason the miracle cure was successful. I was puzzled by this when I first heard the story (I was about 6 years old), because from everything else they'd said about faith, it seemed to be a matter of actually believing a thing as a hard fact without proof. I figured that the sick man might have been thinking all the time, "this probably won't work but what have I got to lose?" I felt slightly relieved at that, because I knew I wasn't capable of internally believing there was no doubt about a thing when there obviously was doubt, but I was likely capable of lowering a sick man through a roof, however objective my thinking was.
There is something obsessive / compulsive about it. I keep checking that my bank card is still in my pocket because I want to be certain I haven't lost it, I feel insecure if I've just used it and can't remember putting it away properly. If I fill in a form, unless I really don't care about the result, I worry if I have the slightest doubt that I've got it 100% right. Problem is, much of the time there's no way to be sure. I get hung up on the tiniest dilemmas, and scour the Web looking for the answers. I don't see it as OCD though, I think it's mostly black-and-white thinking and perfectionism. Checking my pockets occasionally doesn't do any harm. And I'm very receptive to input about what constitutes a reasonable risk and what doesn't, and once I've calculated the risk, my decisions are usually quite sane. I'm aware that I probably "play it too safe," and I'm very interested in anything that can help me discover what matters I can afford to take more risk with. Uncertainty, as well as being something of a curse, is often what makes life fun.