Nature abhors a vacuum.

People often don’t have rooms in their houses that are empty because they’ve already filled it up with stuff.
Clean off a shelf? Watch knick-knacks start to pop up on that shelf.
If you clean a room in a hoarders home, they won’t have an uncluttered room, they’ll just have a new spot to be able to clutter up.

The same thing is often for time. 

People don’t have much free time, and if do get some free time, they’ll fill it up with meaningless activities.
Those activities are the “knick-knacks” of time, and when you do those tasks for a long time, they sometimes are hard to distinguish from the important things you’re doing. Then you can’t figure out why you can never get any free time to get anything important done.

If you can’t have emptiness willingly, you’re likely unconsciously doing things that are cluttering your life mentally or physically.