non-programmers, in my experience, tend to think software is "just that stuff you see on the screen". So if they create some screen mockups of the UI, they think the programmer pretty much needs to sit down at the computer, and do some simple keyboard/mouse clicky-clicky to make the screen match his mockups. and then they're done. To them, it's just visual, and static. They don't understand there are processes, threads, hardware contraints (cpu, memory, disk, network bandwith), libraries, languages, configuration, edge cases, error conditions, etc. I've seen this kind of perspective a lot with non-technical stakeholders, especially first-time clients of software contractors, or first-time managers of software developers.

"Just make it match these mockups!"

Dragging a little Facebook icon into place and poof all the code and edge case handling and database work needed to integrate with Facebook is all done, put to bed, etc. Just put that icon in the right place.