In all productive arts, skill is not the only factor involved in the result. There is 'the Muse'; it comes and goes, whatever it might be, that aspect that sharpens skill, however briefly, to an acute point. There is the material, which has its own constraints and limitations and can resist or facilitate the work. There is also pure aleation, the luck of the art, things just coincidentally falling the right way, a way that could not have been guaranteed or sometimes even hoped-for. Skillful Fëanor, using material of unique kind (the pure light of the Trees, that, as it happened, would soon run out), driven by the fire within, one day in pursuing his craft, was 'on a roll', as we say, everything falling just right, and all these together made the Silmarils, which could never be made again.
It has been noted that in art avant-gardism and kitsch, although often enemies, are in a sense cousins, because they deviate in analogous ways from art proper -- focused wholly on making the thing worth making -- as art-imitating approaches, as quasi-art, as art-mimicries. While art is focused on the work of art, kitsch attempts to mimic the effects of works of art. Joe Carter had a widely read post discussing Thomas Kinkade's painting, which is essentially a discussion of Kinkade's descent into kitsch; Kinkade is a painter of extraordinary talent, but as time goes on the paintings become less exquisite as paintings and more focused on viewer-response. Kinkade had a great talent for painting light-effects; these were part of what really drew people to his paintings. And over time, the paintings increasingly become about the light-effects, to the point of almost exceeding caricature; he became not merely a painter of light, but the Painter of Light (TM), and as Carter notes, his work became derivative and imitative because of it -- although in Kinkade's case it was being derivative and imitative of himself.
Avant-gardism works the same way, but whereas kitsch tries to imitate the effects of the work of art as if they were separable from the integral character of the work of art itself, avant-gardism tries to imitate the disposition of the artist. This is why the twentieth-century saw the explosion of so many forms of 'modern' and 'postmodern' and other kinds of art: it's actually a proliferation of approaches, and much of the history of twentieth-century art can be seen as an almost combinatorial survey of the different ways you can put artistic styles and techniques together. Twentieth-century artists were often less interested in making art than in making up new arts; hence the proliferation of 'manifestos' and 'movements': the shift from focusing on the beautiful to focusing on the new led to an explosion of attempts to try out anything -- and it did end up being just about anything -- that would be different enough to get something new. And thus avant-gardisms tend to isolate out elements involved in making the integral work of art, obsessively trying to purify them into some kind of untainted, or at least infinite, state.
The avant-gardism most associated with the attempt to isolate the aleatory aspect of art is Dada; most work in Dada is almost obsessively concerned with the accidents arising from juxtaposition, the chance felicities, the arbitrary division. Take, for instance, decoupé, also known as the cut-up technique for making a poem. You take a newspaper article, cut it up into words and phrases, put them in a bag; shake to mix them up; and then construct the poem by drawing out the words at random. This is not some mere party game; people often fail to remember the last lines of Tristan Tzara's "How to Make a Dadaist Poem" (Dada Manifesto VIII), which first laid out the technique:
The poem will resemble you.
And there you are - an infinitely original author of charming sensibility, even though unappreciated by the vulgar herd.
It's an effort at the isolation of a pure poetry-insofar-as-it-is-chance-recombination. And this is a genuine part of poetry: most poems involve some aspect of it, and sometimes it is an important aspect, as a chance recombination becomes a seed crystal for something greater. It's not intended as itself a kind of meaninglessness. William S. Burroughs, who was the major popularizer of the technique occasionally noted that what he liked about cut-up technique was that it was like life itself: your life is in some sense a cut-up -- you experience this, and then this other thing, and then that's interrupted by this, and so forth. It's all randomly divided, as different things end up coinciding or interrupting. And yet it's not just a heap of things: your life does not go in any rigid order, it is full of chances and coincidences and random events, but it holds together. There's a meaning in all this chance and randomness that you're not putting there. This is part of art, like it is part of life.
Or take the dadaist sound poem -- for instance, what is perhaps the greatest sound poem, "Karawane", by Hugo Ball:
by Hugo Ball
14th july 1916
jolifanto bambla ô falli bambla
grossiga m'pfa habla horem
higo bloiko russula huju
ü üü ü
schampa wulla wussa ólobo
hej tatta gôrem
wulubu ssubudu uluw ssubudu
Much Dadaist sound poetry finds its root in noisy places with a lot of music, and arises out of the chancy, accidental juxtapositions you get in such places. This gives us the sound-aspect of the poem; Ball's poem was originally written in a different font for each line, which gives a chance difference of look and suggestion to the sounds; and then, of course, sound poetry is to be performed, and there are the chance differences arising from the performance. All of these make the poem to be in some sense meaningless; but the whole point of Dada is that these kinds of meaninglessness are not mere meaninglessness, but actually part of what we harness for meaning in the first place. There is, so to speak, a kind of meaningfulness of meaninglessness interacting with meaninglessness. Change the chance differences, you change the meaning. Compare and contrast two performances of the poem, first by Trio Exvoco:
Second, Marie Osmond giving a looser and more dramatic performance, starting at about 1:37:
The differences in how the poem is recited make a difference, each giving a different sort of meaning-likeness to it. This is operative in every poem. This aspect is usually overwhelmed by other features of the poem, but it can still play a big role, as when different accents change what rhymes or the speed at which you go through a poem will change where the pauses and stresses are. Likewise, the title changes things -- if you treat 'Karawane' as a nonsense word that is part of the poem, as Osmond does, you get one reading of the poem; but Ball was German, and 'Karawane' is the German word for a caravan, usually a desert caravan, although an early alternate title for the poem was "Elefantenkarawane" -- and many performances of the poem attempt to evoke either the German-ish-ness of the poem (reading the words in a more German way, as opposed, for instance, to Osmond's American pronunciation) or the evocation of elephants slowly marching, or both. It also makes a difference whether the famous Ball costumes are involved (Osmond at least gives a representation of them so that people can imagine it while listening if they want) and the context (a vocal performance, which will be focused on the performance and will tend to be appreciated by people with a background of a certain type, or presentation of it as something interesting to a television audience almost all of whom would originally have been getting their very first exposure to anything really like it). All of this will depend on chance: Who picks up the poem to read it, and where, and how, and why? Different juxtapositions give different kinds of suggestiveness.
The chancy character of it is, again, not a void of meaninglessness; it is chance, but meaningful, like a coin toss to decide which way to go, or like spontaneous foolery (to which Ball sometimes compared it). And this is the aleatory aspect of art; Dada is not inventing it but drawing out something that all art contains and focusing almost obsessively on it. And at least some Dada is interesting because chance sometimes does give you the splendid thing, something as good as skill could get you, or even, at times better.
These points, of course, can be generalized to any matter of skill, mutatis mutandis. Part of any skill is handling aleation, and chance contributes its share to the result.