Even in the foodie world, the answer is the same -- HC? Physics!

I'm sure we've all made a batch of chocolate chip cookies once or twice in our lives. The directions on the back of the Nestle Toll House chocolate chips bag seems simple enough, but for some reason, the cookies never seem to turn out quite like they do at some better professional bakeries. I always thought it was somehow due to my lack of fancy kitchen equipment or a secret exotic vanilla extract that pastry chefs kept hidden amongst their inner circles. Turns out, it's none of that. It's simply a matter of letting the dough sit around for awhile:

A long hydration time is important because eggs, unlike, say, water, are gelatinous and slow-moving, she said. Making matters worse, the butter coats the flour, acting, she said, “like border patrol guards,” preventing the liquid from getting through to the dry ingredients. The extra time in the fridge dispatches that problem. Like the Warm Rule, hydration — from overnight, in Mr. Poussot’s case, to up to a few days for Mr. Torres — was a tactic shared by nearly every baker interviewed.

And those sly people over at the Toll House left that out of their public recipe. Sneaky bastards:

“At Toll House, we chill this dough overnight,” she wrote in her “Toll House Cook Book” (Little, Brown, 1953). This crucial bit of information is left out of the version of her recipe that Nestlé printed on the back of its baking bars and, since in 1939, on bags of its chocolate morsels.

Anywho, the original story in The New York Times is quite an interesting read if you've ever tried to make that perfect batch of chocolate chip cookies.