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L'orgoglio folle della razionalità, e dell'individuo solo razionale, fa credere di conoscere quando non può conoscere nemmeno sè stesso.

Gli fa credere di conoscere il funzionamento del corpo umano mentre ne sconosce i più profondi meccanismi.

Gli fa credere di conoscere il cervello umano che è invece l'organo più sconosciuto che esista.

Pur sapendo così poco discetta dei massimi sistemi ed, incredibile a dirsi, parla perfino di Dio.

  .                                              (scritto il 3/2/24)

Here is the translation of the Italian text you provided:
The foolish pride of rationality, and of the rational individual alone, makes him believe that he knows when he cannot even know himself.
It makes him believe that he knows how the human body works, while he is ignorant of its most profound mechanisms.
It makes him believe that he knows the human brain, which is instead the most unknown organ that exists.
Even though he knows so little, he discusses the highest systems and, incredibly, even talks about God.
Here is a more natural-sounding translation:
The foolish pride of rationality leads the individual to believe that he knows everything, even when he doesn't even know himself.
He believes that he knows how the human body works, but he is ignorant of its most profound mechanisms.
He believes that he knows the human brain, but it is the most unknown organ in existence.
Despite knowing so little, he still talks about the highest systems and, incredibly, even talks about God.
I hope this is helpful! Let me know if you have any other questions.