Quadrant II activities are important but not urgent. Because they're not urgent, all but the most effective time managers routinely neglect them. More about these critical forgotten tasks in a moment. In Quadrant III are activities that are urgent but unimportant. Their urgency is generally established by other people, so that dealing with them is an endlessly reactive process.
Most people spend too much time spinning wheels in that process.
This is even more the case when you're stuck in Quadrant IV, dealing with issues that are neither urgent nor important. Effective people stay out of Quadrants III and IV because, urgent or not, they aren't important. I work, to be sure. But also the work that belongs in Quadrant II, the activities whose importance is disguised because they're not urgent.