T he mind requires a degree of chaos in order to properly function. Brain cells can go from acting in predictable ways to a moment of unpredictability which leads, in turn, back to a state of predictability. A good analogy for this is a growing pile of sand. The sand pile grows in predictable ways BUT its collapse is unpredictable.
You can read more about this concept at Disorderly Genius: How Chaos Drives The Brain