Commenter CC (I don't know his name) replied with an excellent example of a planned outcome that paid off, with the PCs deceived a second time by their hated arch-nemesis.
Here's my take on the issue:
Some GMs want to plan and guarantee outcomes because they're control freaks or idiots or dicks who don't care what their players want. They pursue such guarantees whenever they feel like it.
Other GMs want to plan and guarantee outcomes because they know their groups will love 'em. They pursue such guarantees only when an inspiration meets that criteria.
- Still other (most?) GMs are in-between. A little team spirit, a little selfishness.
GMs from all three camps have historically wound up using costly approaches to guarantee their outcomes. Disempowering players is the most common cost, but there are others, like rendering the fiction implausible.
Some GMs who've seen, heard of, or experienced these costs have sworn off guarantees altogether, preferring to play games where outcomes aren't planned.
- Other GMs have kept the guarantees but worked on minimizing the costs. It hasn't been easy. I'm not aware of any published designs that achieve this.
So, when accomplished designers tell an audience of 250 GMs, "Don't plan," they have a point. It's an admonition to the control freaks and dicks and idiots, an alert to the in-betweeners, and a reality check for anyone who thinks minimizing the costs of planning will be quick and easy.
But it's not the end of the conversation. The right outcomes, carefully conceived and brought to fruition, can add great things to play. The costs can in fact be minimized to some degree. How much? Enough? Are there solutions other than years of GM training? System-based solutions, perhaps?
I'm glad the "don't plan" call and efforts are out there. Now let's have some equal passion and effort for "plan right".
Update, Dec. 5 -- I've begun working on ways to support this in the Forge forums. One thread about the general topic, another about resolution, more to come.