There are a thousand ways of creating musical magic. Unfortunately there are at least a million ways of doing the opposite, of creating musical sludge, dreariness, leaden tedium, boring dullness, awkward quirkiness and just simple nastiness. I suppose the meaning of the phrase "ars longa, vita brevis" is that creation is long and arduous, but our time here on earth is brief. The alternate explanation is that while artists may die, their creations are eternal--but that seems a mere happythought to me. What I didn't know until I looked at the Wikipedia article is that the saying comes from the Greeks, Hippocrates, in fact:
Ὁ βίος βραχύς,
ἡ δὲ τέχνη μακρή,
ὁ δὲ καιρὸς ὀξύς,
ἡ δὲ πεῖρα σφαλερή,
ἡ δὲ κρίσις χαλεπή.
In Roman letters
Ho bios brakhys,
hê de tekhnê makrê,
ho de kairos oxys,
hê de peira sphalerê,
hê de krisis khalepê.
Life is short,
and art long,
and judgement difficult.
As Wikipedia points out, "techne" in Greek refers to any kind of technique or craft. So the more obvious interpretation is the correct one.
It is sometimes said, though I forget by whom originally, that genius is nothing but the ability to take infinite pains over every detail. Perhaps this is the explanation for the creation of masterworks. But I know that sometimes when I have done that I have ended up by squeezing every bit of life out of what was originally a decent idea. So perhaps we have to qualify by saying that aesthetic creation often involves not only some original idea, but a great deal of painstaking work in developing and polishing that idea so that it achieves its best presentation.
Sometimes I think that a remarkable amount of the repertoire of high modernism in music, the creations of Boulez, Stockhausen, Cage, et al, illustrates the lengths to which they were prepared to go to avoid the whole aesthetic problem of creation. If you have some sort of mathematical system, as Stockhausen seems to have used sometimes, or really mysterious variation on serialism, as Boulez seems to have been using, or random tosses of coins, as Cage made use of, then you are really substituting an abstract intellectual process for one informed by aesthetic results.
"Techne" for those of us on a different path means what kinds of acoustic effects are we seeking, what do we want the audience to hear and what means do we have available? Unfortunately, the reality is that there are no tried and true ways of creating musical magic as every composer seems to have found different ways of doing so (and different ways in every piece, to boot). Experimentations may indeed be perilous, but there ain't no other way, I suspect. This is one reason why Steve Reich's music seems to ring true for me: it bears every sign of being the result of considerable experimentation on the instruments. He has worked everything out and gotten the results he was looking for in sound. Whether you like it or not, is up to you, of course, but you can't say it wasn't an honest effort aesthetically.
But back to how we create musical magic. I suppose it really comes down to trying different things and listening to the result. It is partly in the imagination and partly in the hands (or voice, or breath). Music has effects on different levels: intellectual, emotional and physical. We might even try and locate these levels in the structure: a lot of the emotion (by which I don't mean ordinary emotions like love and hate, but more musical moods) is transmitted with the melody (and some harmony). A lot of the intellectual level is found in the harmony, but also in the counterpoint. And it is usually the rhythm and meter that reaches us on the physical level. Steve Reich, for example, achieves some of his most interesting effects by changing the meter, but not the rhythm, of a melody or by relocating where the downbeat is.
It is often through restraint that powerful effects are created. Beethoven's incredibly tight focus on three tiny aspects of the theme of the Diabelli Variations over all thirty-three sections is the source of much of the power of that music. But other powerful effects are achieved through simply piling on more and more and more, as in the first movement of the Symphony No. 7 by Shostakovich where an eleven minute crescendo starts with a very quiet tattoo on a snare drum and ends with the whole orchestra making as much noise as they can. And no, you have to hear in in concert because these dynamic extremes are beyond the capacity of most recording processes, not to mention your home stereo.
It turns out that musical magic is largely about creativity, which, it seems, involves being creative. Heh!
Let's listen to the Diabelli Variations by Beethoven. I discussed this piece in some detail in this post. The pianist is Grigory Sokolov: