Originally Posted by
PairO'Dice Lost
I don't think ascribing things to nebulous "innate talent" is a satisfying solution, really, since that posits that all PCs (or just those that want to multiclass into a casting class, perhaps) happen to be drawn from a pool of exceptional individuals, and while many PCs have that kind of backstory there's plenty who have the "just an ordinary person thrust into extraordinary circumstances" backstory and don't want to discover midway that they've been special all along.
What might make more sense is to say that exposure to magic (both physically being exposed to it and merely encountering and studying it) improves your ability to create and open spell slots. They're magical channels in your mind and body, after all, so having magic flow through you would help with that, and being able to recognize the sensations of magic, see what other magic-users are doing, and so forth can help guide meditations and point out blind spots in practice regimens.
This helps explain why fighter PCs can pick up wizardry faster than an apprentice wizard if they want to--if you're repeatedly getting fireball'd and cure wounds'd on a daily basis and running into all sorts of strange magical fields, you can skip a lot of the basic regimens because you don't need several weeks to sense your chakras (they're still smarting from that behir's breath last weekend, thankyouverymuch), a month to figure out how to totally clear your mind (that mystical fountain on the third level of that tomb had a fairly similar effect), and so forth. It also explains why non-wizard arcanists might congregate in guilds (just being around experienced spellcasters is helpful for apprentices even if you don't directly learn anything from them), why wizards build towers (it concentrates lots of magic to make it easier for you to open your spell slots), and other setting conceits.