In music, complexity is wrought through pacing, density, distances between one note and the next, and so forth. Now, I'm not a musician, at least not one worth the title, nor a music theorist. I can't read music. I didn't go to band camp. I really don't know HOW music works, I just know that it DOES work. It amazes me (being easily distractible) that someone could play a complex piece of music flawlessly, every single time it's played. How is that even possible? My brain just can't do it.
One particularly amazing composition from Frank Zappa's oeuvre is The Black Page (parts 1&2). It is an incredibly complex piece, born out of the idea of unconquerable complexity.
This is just the drum part, mind you. When put together with a variety of other instruments, it becomes almost incomprehensibly complex, and each part must be precisely synchronized with all of the others, or it dissolves into pure chaos.
Still, this is only scratching the surface of the theoretical complexity of Vancian magic, the underpinning of the magic system in DCC. It explains why Vance's descriptions of mage's abilities were in terms of how many such compositions his or her head could hold at once, and how, once in the mind, they sat heavily, uncomfortably. Given that composers and musicians who work professionally probably know hundreds of songs, and can play them pretty much on command, the idea of a "professional" wizard only being able to hold three or four spells in his or her head speaks to a level of complexity that is truly staggering. It is the equivalent of the wizard playing even something relatively "simple" like this, on all of the instruments at once, solo. One missed note and the spell fails, shocking your mind. One dropped or reversed measure and you're growing a second head out of your ass and a tentacle where your wang used to be. Bad Things happen when you fuck it up.
So, yeah, magic is so incredibly dangerous that it makes juggling canisters of nitroglycerin seem like a child's game in comparison.
Summoning magical energies is arduous, expensive, and dangerous. No wizard does it lightly. As a result, there are no mundane magics, no spells used simply to light a corridor, for example. Use a torch, fool; it is much safer! (DCC Core Rules, p. 106)