Neat explanation for D&D spells

They're mind parasites. [Link]

The casting of magical rituals was once a lengthy and time-consuming process; one which often required the combined efforts of entire covens or wizard circles to complete. All of that changed, however, when wizards first discovered spells.

The earliest spells were dangerous and unstable — parasitic horrors from a primordial proto-plane of raw magical essence which feasted memetically upon the sanity of those they infected. But whether by accident or design, a small band of wizards managed to tame the spells to their own purposes. With proper training, they learned that these living parasites could hold complex rituals in a state of pressurized memetic potential. And then, by infecting themselves, they discovered that they could release the entrapped rituals upon command.

Magical rites that had once taken hours, days, or even months to cast could now be unleashed in minutes. (And later, as their arts improved, in mere moments.) The world was transformed.

The parasites, of course, were consumed in their casting. And so, every morning, wizards find themselves preparing fresh spells and then infecting their minds with them. It takes years of practice to perfect the finely honed balance required to sustain even a single spell-parasite in your mind without being driven mad by its thought-consuming proclivity. The ability to sustain multiple spells in that state of mind-rending follows more quickly, but it is always a delicate balance between power and madness for those who would follow such a path.