When after a third statement a student forgets what was the first one, this student will not be able to design a complicated train of thoughts.
Another important professional ability - multi-tasking - is also based on the highly developed brain structure. Multi-tasking is merely an ability to switch between different mental tasks. When a brain is processing information related to one task, the regions in a brain devoted to another tasks remain idle. When needed, one can make a switch, make another region idle. But that is possible ONLY when a brain has such a capability. If switching to another task erases information about the previous task it only leads to a growing number of incomplete tasks.
And the ability to become a moral person is also available only to people with a developed brain. In order to follow "The Golden Rule" one needs - at the minimum - to be able to place himself/herself in someone else's shoes. That requires imagination. Imagination requires developed brain. In general, imagination is the most important mental ability of all. No type of designing is possible without imagination. Unfortunately, mass education not just ignores development of imagination, it stifles it. And watching TV shows, movies, or paling video games do NOT help ID (imagination development). The best three practices for ID are (1) reading, (2) writing (or story telling), (3) games required role playing (e.g. a theater).
Every healthy person, if starts learning early, can learn how to juggle with two or three balls. Learning that at an old age is much harder, and for some people even impossible.