It is common to have fears of anything that lies outside those norms. Anything that is different, inconsistent, unpredictable, unexplainable, and extraordinary is often considered dangerous and unsane. Particularly anything that is moving rapidly in forceful but totally unpredictable ways can easily be considered insane. Commonly people have built a small element of unpredictability into their lives. A few surprises and a little weirdness becomes a spice of life.
Different people have different degrees to which they tolerate unpredictability.
But almost always there will be a limit that cannot be crossed without fear of insanity. Now, really all of this is a rather upside down view of things. Fixedness and limitation are passing for sanity. Uncontrolled motion passes for insanity. The truth of the matter is that the true nature of things always is dynamic.