Usually when thinking about customers we can think of end-users of a company's products or services, or the sponsor (or whoever is paying you.) If you think like that you usually focus on what is most important.
Sometimes (okay, usualy) you can get stuck dealing with the stakeholders wants and needs and they become the focus and the main part of the work involved in getting to the right solution.. It feels like the pareto principle is at work, and that's a trigger for optimisation.
To streamline the amount of non-trival, but non-core requiremets that you need to deal with you can try any number of requirements categorisation techniques. My current favorite is ranking requirements.
It is an excellent prioritisation tool, facilitaes iterative development and helps senior management's goals be put in the right context in relation to middle and front-line management goals.
Frankly, it gets a good conversation going among business stakeholders, top to bottom. And once you have an aligned vision of the product amomng your business stakeholders, many of your potential project problems are resolved.
Photo by Bashed CC @ Flickr