Herbie is like that friend you have who doesn't tell you that your fly is down because he doesn't want to embarrass you. Of course, then you walk around all day with your fly down and you're even more embarrassed. That's pretty much Herbie's whole story.
See, Herbie is a mind-reading robot—he was a pure accident and he's one of a kind. But because he's a mind-reader, he has a slightly expanded view of the what the First Law should be, a view which might include "hurt feelings," "deflation of one's ego," and "the blasting of one's hopes" (225). That is, Herbie has to avoid hurting people, which means he has to avoid hurting people's feelings. Which, to him, means that he has to tell people what they want to hear. So, if you had your fly undone, Herbie might not tell you, because it might embarrass you.
Now, this raises a really interesting and important question: who gets to decide what it means to hurt someone? The robots can't hurt people, but it seems as if they get to figure out what that means for themselves. We'll see something similar to this with the Nestor robots in "Little Lost Robot" when it comes to the second test that Calvin devises; that is, in that case, the Nestors talk with each other and decide it's better not to kill themselves needlessly. But poor Herbie is one of a kind; maybe if there were other mind-reading robots, they could talk over things and come to a better solution. And we think there is a better solution; after all, couldn't Herbie be taught to think about things in the long term? That is, if he told Calvin that Ashe was marrying someone else at the beginning of the story, that would hurt her, but it would be less hurtful than letting her find out the truth at the end of the story. So Herbie's really got two problems: he cares what people think; and he has no one to discuss these issues with. In fact, he can't even talk about this with people since that would probably result in their hurt feelings. So no one knows what he's going through (80).
So, what does this robot tell us about robots? That they always try to do the right thing, but they don't always successfully do it.
By contrast, check out what Susan Calvin does at the end of the story—she intentionally drives Herbie insane. Herbie may let you walk around with your fly down, but that's much nicer than what Susan Calvin will do to you.