When you study, say, biology, you'll probably learn about all the wrong turns that very smart people made along the road to where we currently stand: self-moving principles in Aristotle; vitalism; spontaneous generation; enzymes as living organism; and many many more. That background gives you a sense of how hard it is to be right, and the importance of modesty and self-doubt.
Whereas with computer science, what you learn about is the (relatively short, historically speaking) string of amazing successes in the field. And the more practical side of it (e.g., what software we produce for consumers) is even more unique in having this underlying exponential growth (Moore's law) foisting it up, and drastically changing at every moment what is possible, so that in fact there are very many opportunities that no one thought about simply because they weren't opportunities three years earlier.
And then programmers start thinking that, not only is improvement easy in all fields, but also the fact that other fields don't have as much to show for themselves by way of these improvements (whereas they do) just indicates how much better and smarter and innovative they are, and how in light of this it really isn't surprising at all that they may, even as outsiders, have a lot to contribute to any given field.