Consider the user supply chain too

I am doing some research for an entrepreneur in Salt Lake City for which I need to purchase three back belts. Because of the purchasing system at the university (a design challenge for another time), I would like to order the belts online or by phone, but pick them up in the store (to eliminate the delay and cost of shipping).

Home Depot does not support this. Lowe's does. And so even because Lowe's is 20% more expensive, they got my business. They understand my supply chain process and support it. Even though Home Depot has a reputation for having a very efficient supply chain of their own, they apparently have not considered their users'. Their loss!!

which requirements are worth supporting??

There are many features that would be nice to have. For example, how many people press the wrong button in elevators once in a while, and then have to wait while the elevator stops at the wrong floor? It would be nice if there were some kind of undo function. Maybe you could press the wrong button a second time to turn it off.

But here is the question. How important is this to the user experience? And are there consequences to adding it that could take away from its value? For example, would it add to the cost of the design? Would there be a learning curve during which other errors would occur (hitting the button twice on purpose to "make sure" we pressed it). Would there be other permanent errors that could be introduced (someone intentionally turning off other passengers' floors because they are in a rush).

It is this set of tradeoffs that are necessary to decide when a design feature really makes the system more effective.