Humans are meaning making machines.
We spend a lot of our energy creating reasons and justifications and rules to define the world we live in, and to guide us in our choices.
"Good people tell the truth."
"Vegetarianism is ultimately better."
"It shouldn't rain every day on my vacation."
This works until something happens that we don't expect, or doesn't fit in the version of the world we created in our minds.
Then we become upset, angry, depressed. When we can't let go there is a tendency to act aggressively towards the outside world or ourselves, in disbelief that things haven't gone as expected.
Living without aggression is the discipline to always be flexible, to let go of even our most deeply held beliefs in the face of evidence the the world is different than the stories we create about it. Even if the thing we are faced with is something totally fucked up, something that just seems completely wrong, we let go of our beliefs lightly, like a butterfly we caught in our hand and eventually let go.
Flexibility emerges from an understanding that everything we see and describe in the world, if we really look underneath the surface, ultimately has no permanent substance. In the end there's nothing there.
And yet living without meaning is impossible. We keep making new stories and new meanings, understanding that none of them is ultimately true, this sentence included.