Complex sentence: Estraven is one of the few Gethenians who believes Ai, and he attempts to help him from the beginning, but Ai's inability to comprehend "shifgrethor" leads to severe misunderstanding between them.
Split into simpler sentences: Estraven is one of the few Gethenians who believes Ai, and he attempts to help him from the beginning. However, Ai's lack of understanding of "shifgrethor" leads to severe misunderstanding between them.