In this analogy, Rocks are ‘big things’ that are important, possibly scary, and time consuming – but drive the most value. You probably have somewhere between 2 and 8 of these on your plate at any given moment in time.
Pebbles are small, administrative (or worse, procrastinatory) tasks; typically these are numerous, constantly appearing, and often recurring.
If you catch yourself looking for Pebbles to move around whenever you see a Rock, that’s a problem.
Matt Fried 