You've probably heard it said before, that quantifiable achievements are an important component of a solid resume. They lend credibility to claims that otherwise might fall flat and – at the very least – fail to separate you from the competition. People, in general, struggle to speak about their work history in these measurable terms. Many others simply feel that quantifiable achievements don't apply to their work; they move through their professional careers with the belief that only people in, say, Sales need to think about including such metrics. Nearly every position – with very few exceptions – has an impact on the organization/company in a measurable way. The problem is that professionals in many positions aren't really programed to look at their work in terms of how it boosts success.
Quantifiable achievements are difficult for many people to wrap their minds around. Agreed. We need to back up a bit though.
Most people struggle to speak in terms of accomplishments – never mind quantifiable accomplishments – on their resumes. So, the first step is to get out of task/responsibility mode when thinking of your world of work.
Don't make the mistake of turning your job descriptions into your resume entries. Look at your resume as valuable real estate. Your first goal should be to minimize the valuable space that you dedicate to responsibilities."But I want them to know that I XXX," I hear time and time again. Don't worry... There are very efficient ways to speak to responsibilities without making them the basis of your entire resume. Ideally, you'll have such powerful achievement-centric bullets that the associated responsibility will be inferred.
So, when you can't get out of responsibility mode, ask yourself: "To what end did I do XXX?" If you absolutely can't pull something quantifiable out of the responsibility, at least speak to the end result – the accomplishment.