I think the most correct way to phrase this would be that the more complicated something is, the more likely it is that you believe some falsehoods about it, or that there are entire areas that you didn't consider at all. And people are often very bad at recognizing complexity upfront.

One extreme example that comes to mind is people asking contractors on websites like Upwork to implement a clone of google.com, with some ridiculous offers under $1000. The rationale being that google.com only has a logo, text field, and two buttons, so it shouldn't be too hard to make.