Someone on my team was facing a crisis and needed my help. I had room in my calendar, so I could spend a few hours to help them out. 

Slack in my calendar also means that I can explore curiosities and opportunities that could turn into something meaningful and significant. I can have leisurely strolls, or brunches that turn into day-long adventures. 

We are in a world obsessed with productivity and efficiency. Being busy with a packed calendar seems like the best way to succeed at work and in life. But high efficiency often means low resilience and innovation, because of low capacity to fight fires or uncover new possibilities. And not to mention, the risk of debilitating burnout. 

Gaps in your days and weeks because they are essential - to survive and to provide fertile ground for growth. Create and guard them.