How we cite our quotes: (Part.Chapter.Paragraph)
Quote #1
Oh, we can populate the dark with horrors, even we who think ourselves informed and sure, believing nothing we cannot measure or weigh. I knew beyond all doubt that the dark things crowding in on me either did not exist or were not dangerous to me, and still I was afraid. I thought how terrible the nights must have been in a time when men knew the things were there and were deadly. But no, that's wrong. If I knew they were there, I would have weapons against them, charms, prayers, some kind of alliance with forces equally strong but on my side. Knowing they were not there made me defenseless against them and perhaps more afraid. (2.3.2)
In Steinbeck's view, even things that you know aren't real can be pretty scary—apparently because, even if you "know" they aren't there, they still might be there and, if so, you'll be defenseless against them. Really, this is just an example of how the mind can spiral in isolation, right?
Quote #2
On the long journey doubts were often my companions. I've always admired those reporters who can descend on an area, talk to key people, ask key questions, take samplings of opinions, and then set down an orderly report very like a road map. What I set down here is true until someone else passes that way and rearranges the world in his own style. In literary criticism the critic has no choice but to make over the victim of his attention into something the size and shape of himself. (2.3.61)
As we've already discussed elsewhere, Steinbeck played a bit fast and loose with the truth in this "travelogue," and his musings about truth (and whether it's possible to convey and embody it in writing) might represent a wink wink moment, a kind of nudge toward not really thinking about what Steinbeck writes in terms of strict notions of truth and fiction.
Quote #3
Joe and I flew home to America in the same plane, and on the way he told me about Prague, and his Prague had no relation to the city I had seen and heard. It just wasn't the same place, and yet each of us was honest, neither one a liar, both pretty good observers by any standard, and we brought home two cities, two truths. For this reason I cannot commend this account as an America that you will find. So much there is to see, but our morning eyes describe a different world than do our afternoon eyes, and surely our wearied evening eyes can report only a weary evening world. (2.3.62)
Again, we've definitely covered this general topic elsewhere (and this specific quote in "Literature and Writing"), but basically truth is kind of a relative, situational, subjective thing for Steinbeck, and he just doesn't think that two people can necessarily come up with a consistent "truth" about a place. That said, it doesn't mean someone is lying or anything—different people just have different experiences at different times.