Maybe chaos theory isn't your cup of tea. Deterministic nonlinear systems and the factors used to describe them aren't for everyone. The "butterfly effect" really is a thing though, and the Luke Voit trade provides some compelling evidence.
Some of the best win-win trades occur when competing organizations have the right mixture of respective needs and resources. Think of this as an occasion of serendipitous confluence. The Cardinals needed to fortify their bullpen, and they had an extra 1B with some power just sitting around in Memphis. The Yankees had some spare pitching parts, but they needed at least a rental 1B with some pop. Given these considerations, a swap of Voit and international bonus slot money for Giovanny Gallegos and Chasen Shreve made sense for both sides.
Voit then goes on to hit 14 HR in 148 PA with the Yankees, and Shreve is now doing something that doesn't involve pitching for St. Louis. Whatever.
The point is that moving Voit changed the depth chart at 1B for the Cardinals, and it had the unintended consequence of creating space for Paul Goldschmidt. Not that the space had to exist already. Making room for Goldschmidt is a no-brainer, but timing and sequence were important here.
When the Cardinals moved Voit, the 1B market wasn't held hostage by a big available name. There were no names like "Goldschmidt" floating around to affect leverage or suppress trade values. Had they held onto Voit AND then gone on to obtain Goldschmidt, the leverage/value proposition likely would have been greatly affected. Teams interested in Voit or even Jose Martinez could have approached the team knowing that 1B was locked down. Even in that scenario, the Cardinals would not necessarily have to move Voit, but the change in perceived value would not have been a good thing.
In an alternate timeline, Voit instead hits 14 HR in 148 PA with the Cardinals, and Goldschmidt never becomes a Cardinal.
In our current reality, the Cardinals signed Goldschmidt to an extension, and it's plausible that the extension is simply another end point resulting from the Voit Effect.
Actions have consequences, and it's impossible to predict with absolute certainty what those consequences will be. However, that's no reason not to make predictions with zero certainty, and I'm here for it.
Reckless prediction with zero certainty: Many will look back in 5+ years and think the Cardinals would've gotten a lot more bang for their buck with Voit instead of Goldy.
I just hope that I'm not one of them.