It is intrinsic to the nature of the programming task that you cannot do it without having a large number of things in your head at once. OK, there are programming-related tasks that can be done getting into the specifics less - otherwise sites like this could not happen. But estimates that I have seen is that about a third of the work of a professional programmer is work that you cannot begin to be productive at unless you have already had 15-20 minutes getting a good "mental flow" going.

In other words the same principles that make interruptions such a productivity killer also make it impossible to produce useful software out of a million programmer's "wasted interrupt time".

Book recommend: if you haven't read Peopleware, do.

UPDATE: I think of this place as being somewhere you go to get the kind of advice you can give based on small pieces of code which zby commented on below. He might have a different vision though.