Here's a nice, simple presentation that breaks down what media planning used to be, what it's evolved into, and why. It also breaks the core of media planning down nicely: we're working with principles now, not rules.
The latter was great for creating barriers between companies and people, which was highly profitable, but not realistic or sustainable. The former is more vague and harder to quantify, but it forces you to stay intimately connected to users and innovators because they are the ones whose behaviours, sentiments and feedback will lead you.
How hard can that be? About as hard as you, on your own, trying to be a better person every single day of your life. Except scaled. Enormously. *shrug*
And in the end, doesn't that make sense? We've spent years trying to get people to feel emotions for brands as if they were human, concurrently creating laws that treat companies as if they are autonomous entities. Forcing them to comport themselves according to the standards of Ethical Man seems like a natural expectation.
That was an enormous digression. Sorry, guys.