What do you want to achieve? This is probably the most important question you can ask someone who comes to you with a request. People (usually) know what they want, but that does not mean they know what they actually need. 
Let me try to put this into context; I work as an operation manager for a mid-sized IT company, which means people come to me asking for resources. And by people, I mean developers, and by resources, I mean anything from a new server to a firewall opening.
It is in this context; I have learned to ask the question: what do you want to achieve?
Most of the time, what they want is also what they need. But occasionally, what they ask for just makes no sense, like: “can you create a subdomain pointing to a specific path on the webserver?”  Even if they do ask for something sensible, they still might not know what they really need.
In this example, what they wanted was to display a specific landing page depending on the subdomain that was used. The solution, if you wonder, is to have a piece of code that checks the incoming http request header rather than trying to make DNS into something it is not.
It is not that developers are stupid, on the contrary, developers actually apply a great deal of logic to their thinking; leading to assumptions like: “If a domain name points to a website, it should also be able to point to a specific path of a website.”
The point is: if you ask someone what they want to achieve, you can potentially save yourself and others from wasting time doing the wrong things. And time is the most valuable resource we have.
It is such a simple question, yet so powerful: What do you want to achieve?
 A lot of people struggle with what they want in life – as do I – but in this context I am talking about when people ask for something specific.
 This is of course a made-up example (or is it?)