Focusing is about saying no. And you've got to say no, no, no. And when you say no you piss off people.
Given my new role as VP of Product Development, I'll get to say no many more times than before. As Steve Jobs so eloquently said it many years ago, when you say no you piss off people. Especially top managers are really bad at handling no. Depending on how important yes is to them, they either silently resent it, actively scheme against you, our outright twist your arm until you say yes. Unless you're on verge of being fired, you always have a few no's at your disposal. But you should be careful how you spend your no's, as their number is finite and with every no your political status and importance in the organization diminishes.
A great alternative to saying no is saying "yes, but..." For example, when being asked by sales to create a report B, you can either say "no" or you can say "yes, but in that case we have to postpone development of report A, that you've requested last week", which will shelf in most cases the request for report B. Another great alternative to saying an outright no is to say no but provide alternative solution to the problem. In case of aforementioned example, we can soften the no by saying "we cannot do report B, but there's report C which is almost what you want and solves most of your problems". There are several more techniques how to make no more acceptable, but at the end of the day there will be cases when you'll have to say an outright no. And when you do, you'll see in people's eyes them silently saying "oh, what a jerk".