I've found that in some cases it comes from not being able to understand what you do here as Office Space would say.

If you were a plumber, she'd have an easy answer when talking to her friends about what doubled112 does. Plumber is a job everyone understands at a basic level; most of the trades are because you can point to a finished product. "He builds things like that."

Sometimes an analogy can help; I've definitely told people I'm an internet plumber and that seems to satisfy their curiosity.