Δεν είναι φυσιολογικό να φοβάσαι μην κάνεις λάθος σε κάθε λέξη.

Because Greek often uses the neuter singular adjective in impersonal expressions, where English uses it is + adjective.

So:

• Δεν είναι φυσιολογικό... = It isn’t normal...

There is no real concrete noun being described here. The whole idea να φοβάσαι... acts like the subject, and Greek treats that kind of idea with a neuter singular adjective.

This is a very common Greek pattern:

• είναι + adjective + να + verb

It means something like:

• it is normal to...
• it is difficult to...
• it is important to...

So here:

• Δεν είναι φυσιολογικό να φοβάσαι...
• literally: It is not normal to be afraid...

Since Modern Greek does not use an infinitive the way English does, it usually uses να + verb instead.

Because after είναι φυσιολογικό, Greek normally uses να + subjunctive-style verb form.

So:

• Δεν είναι φυσιολογικό να φοβάσαι = It isn’t normal for you to be afraid / to be afraid

If you said only Δεν είναι φυσιολογικό φοβάσαι, that would be ungrammatical.

In many places where English uses an infinitive like to be afraid, Greek uses να φοβάσαι.

This is about aspect.

• να φοβάσαι shows an ongoing, repeated, or general state
• να φοβηθείς would suggest becoming afraid once or a single complete reaction

In this sentence, the idea is not one isolated moment of fear. It is a general pattern:

• being afraid
• constantly worrying
• feeling nervous all the time when speaking or writing

So να φοβάσαι fits better.

Not exactly.

After verbs of fear like φοβάμαι, μην often introduces the thing you are afraid might happen.

So here:

• φοβάσαι μην κάνεις λάθος
• means you’re afraid you might make a mistake

In this structure, μην is often best understood as:

• that
• in case
• lest
• that ... might

So it does not function like a simple straight English not here.

Compare:

• Μην κάνεις λάθος! = Don’t make a mistake!
  Here μην is true negation in a command.

But in your sentence:

• φοβάσαι μην κάνεις λάθος
• = you’re afraid you may make a mistake

Different function.

Here it functions as subjunctive, because it is introduced by μην in a dependent clause after a verb of fear.

One thing that confuses learners is that in Modern Greek, many subjunctive forms look exactly like indicative forms. The form itself may be identical, and the particle tells you how to read it:

• να / μην + verb → subjunctive environment

So in this sentence:

• μην κάνεις λάθος

you should understand κάνεις as part of a clause meaning:

• that you might make a mistake

not as a plain indicative you make.

Greek very often uses the fixed expression:

• κάνω λάθος = make a mistake / be wrong

The singular λάθος is completely natural when talking about the possibility of making a mistake in a general sense.

So:

• μην κάνεις λάθος = that you might make a mistake

If you wanted to emphasize many mistakes, you could use the plural:

• κάνεις λάθη = make mistakes

But the singular is the normal idiomatic choice here.

Because κάθε in Greek normally goes with the singular, just like English every:

• κάθε λέξη = every word
• κάθε μέρα = every day
• κάθε φορά = every time

So σε κάθε λέξη is exactly what you would expect grammatically.

Literally, it is in every word or on every word, but in natural English the sense is:

• in every word
• with every word
• on every single word

It means the speaker is worried about making a mistake again and again, word after word.

The preposition σε is normal here because Greek often says:

• κάνω λάθος σε κάτι
• make a mistake in something / on something

So:

• κάνεις λάθος σε κάθε λέξη
• = you make a mistake in every word

Because Greek usually drops subject pronouns when the verb ending already shows the person.

Here:

• φοβάσαι = you are afraid
• κάνεις = you make / you might make

So εσύ is not needed.

If you added εσύ, it would sound more emphatic, like:

• You, specifically, are afraid...

But in a neutral sentence, Greek normally leaves it out.

Yes. After φοβάμαι, Greek very often uses μήπως as well.

So these are both possible:

• φοβάσαι μην κάνεις λάθος
• φοβάσαι μήπως κάνεις λάθος

Both mean roughly:

• you’re afraid you might make a mistake

For many speakers, μήπως can sound a bit more common or conversational in this kind of sentence, but μην is also correct and natural.

Sometimes yes, but usually here it is better understood as:

• It’s not normal
• It isn’t normal
• It’s not healthy/typical

The word φυσιολογικός / φυσιολογικό often means normal in everyday Greek, not only natural in the strict English sense.

So in this sentence, the best reading is:

• It’s not normal to be afraid you’ll make a mistake in every word.