Repetition is based on body rhythms, so we identify with the heartbeat, or with walking, or with breathing.
Karlheinz Stockhausen, a composer and musical theorist, was obviously talking about music. But repetition is a fact of every aspect of life, and every aspect has its own rhythm. Tomorrow follows today and another day will come after tomorrow and so on (unless, of course, Armageddon descends upon us). You take one step, then the next, and many others after that until you reach your destination. One sip of water is often not enough and you must chew your food more than once. You hardly ever think about these daily occurrences , partly because they are repetitive or recurrent.
In art (about which I know something) and music (about which I know zilch except as a dedicated listener), creating rhythm relies on repetition. In fact, repetition is an underlying principle in all arts. It is the basis of patterns (See here and here.)
Using patterns in art achieves harmony because the human gaze recognizes and tends to follow repetitions in lines, colors, forms or shapes (some basic elements of art). Those repetitions are generally reassuring and, maybe, they also appeal to our sense of beauty (whether innate, cultural, or even idiosyncratic).
True, repetitions are not always reassuring. As you well know, they can be boring; and, sometimes, they are downright annoying and you want to get away from them.
In addition to harmony, patterns also produce movement through repeated elements. When you see that familiar photograph of trees that decrease in size away from you, doesn’t it suggest physical movement?
But look at this abstract painting by Kandinsky. Movement is everywhere in this painting, although the easiest for me to see is that of circles of different sizes whose placement all over the canvas suggests continuous motion. And, yet, because I don’t recognize a familiar pattern (you may), I also find it a bit chaotic. You may, in fact, focus on entirely something else which you gives you the sense of movement.