The Law of the Minimum seems metaphorically relevant. "Growth is controlled not by the total amount of resources available, but by the scarcest resource."
Intelligence, speed, time, energy, charisma, money, able-bodiedness, a like-minded community, etc.: any of these may be someone's limiting factor.
On the other hand, sometimes one resource can trade off for another. There are a lot of examples of this in computational complexity where one can use up less memory if one is willing to use a slower algorithm or if one is willing to use more memory one can get more speed. These aren't the only examples.
From Scott Adams Blog
The article really is about speeding up government, but the key point is speed as a component of smart:
This shifts the focus from the ability to grasp and think through very complex topics (includes good working memory and memory recall in general) to the ability new topics quickly (includes quick learning and unlearning, creativity).
This also changes the type of grit needed. The grit to push through a long topic versus the grit try lots of new things and to learn from failures.