"I am fine, he is not fine."
Translation:Ben iyiyim, o iyi değil.
Is the "ben" at the beginning absolutely necessary? I didn't use it, and it was marked as a mistake.
The only reason why you would say such a sentence is to compare the state of being of two different people. So it only makes sense to actually use them in order to accentuate them. It sounds weird without anything.
On a side note, I would also stress the pronouns in the English sentence and say: Me, I'm fine; But him… he's not all that fine. or something of that nature.
iyi is the original word for "fine/good", so when you want to say "I am fine" you have to add the suffix "im" for ben. So it would technically be Ben iyiim but since two vowels are next to eachother we add the buffer letter "y" so it becomes "Ben iyiyim".
Pronouns are optional if there is only one in the sentence, but if we are comparing/contrasting two people (or groups of people with "biz" and "siz"), we need to include them both.