Difference between a hobby project and a product

One of the most important lessons an engineer learns is that a going from a demonstration prototype (i.e. "hobby project") to a product that other non-engineer people can use requires a lot of additional work. I would say that prototype to product transition requires as much work as creating the protoype.

A product

• is well tested and can work under a wide range of conditions (this is the main cost difference because additional testing reveals previously unknown weaknesses and will force you to make major design changes)
• anticipates internal errors / environmental anomalies and has mechanisms in place to recover gracefully
• anticipates user error and guides the user when he does something wrong
• has an intuitive user interface (i.e. people don't need to ask an engineer how to operate it)

A novice thinks he almost has a product when he demonstrates basic functionality. The wise one knows that he has only covered half the distance.