Learn Farsi: این معیار نشان می‌دهد که یکی فایده دارد و دیگری خطرناک است. - This criterion shows that one has a benefit and the other is dangerous.

This is the core structure for contrasting two items in Farsi. یکی means "one", and دیگری means "the other". You use them as a pair exactly like "one ... the other" in English when you want to compare or contrast two things that are already the topic of conversation.

Why does the Farsi use فایده دارد instead of an adjective for "beneficial"?

In Farsi, the concept of being beneficial is often expressed with the verb داشتن (to have). So instead of saying "is beneficial", the sentence says فایده دارد, which literally translates to "has benefit". This is a very common pattern where English would use the verb "to be" plus an adjective.

Why is the verb for "shows" made of two words (نشان می‌دهد)?

This is a compound verb. It is made of the noun نشان (meaning "sign" or "mark") and the verb می‌دهد (the present tense of "to give"). Literally translating to "gives a sign," this combination is the standard Farsi way to say "shows."

What is the function of که right after the first verb?

Here, که functions exactly like the English word "that" when connecting two clauses. It links the main action (این معیار نشان می‌دهد - This criterion shows) to the fact being shown. While English speakers sometimes drop the word "that" in casual speech, in Farsi, که is almost always kept.