Se mi pravus ĉiam, mi neniam erarus, sed tiel ne estas.

Because the sentence is talking about an unreal or hypothetical situation.

• -us is the Esperanto conditional mood
• It is used for ideas like would, would be, would happen

• In Esperanto, in a contrary-to-fact if sentence, it is very common to use -us in both parts:

• Se mi pravus ĉiam = If I were always right
• mi neniam erarus = I would never make mistakes

So the structure is very natural Esperanto for a hypothetical idea that is not actually true.

No. -us does not mean past tense.

That is an important difference from English.

In English, we often use a past-looking form for unreal conditions:

• If I were always right, I would never be wrong

But in Esperanto:

• pravus does not mean was right
• it means would be right / were right in a hypothetical sense

So -us shows mood, not time.

The sentence is about a present/general unreal idea, not the past.

Because Esperanto often uses a simple verb where English uses be + adjective.

Here:

• pravi = to be right
• erari = to make a mistake / be mistaken / be wrong

So:

• mi pravas = I am right
• mi eraras = I am mistaken / I am wrong

This is very normal Esperanto style. It is shorter and more direct than saying something like mi estas prava or mi estas erara.

Those adjective-based versions may be understandable, but pravi and erari are the more natural choices here.

Because neniam already contains the negative idea.

• neniam = never

In Esperanto, words like neniam, nenio, neniu, and so on usually do not need an extra ne.

So:

• Mi neniam erarus = I would never be wrong / make a mistake

Adding ne as well would be nonstandard here.

For an English speaker, this is worth remembering: Esperanto usually lets the n- word carry the negation by itself.

Literally, it means something like:

• it is not so
• it is not like that
• that is not the case

Here tiel refers back to the whole previous idea:

• that situation where I am always right and never mistaken

So:

• sed tiel ne estas = but that is not how things are / but that is not the case

It is a very natural way to reject the hypothetical idea and return to reality.

Yes. Both are possible.

Esperanto word order is fairly flexible, especially with adverbs like ĉiam.

So both of these work:

• Se mi pravus ĉiam
• Se mi ĉiam pravus

The second one may feel a little more natural to many learners, because English also tends to place always before the main verb in this kind of sentence.

But the version in your sentence is perfectly understandable and correct.

Yes, you can think of one as being understood.

Esperanto often allows:

• Se ..., tiam ... = If ..., then ...

So the sentence could also be written as:

• Se mi pravus ĉiam, tiam mi neniam erarus...

But tiam is often omitted when the relationship is already clear.

That means the original sentence is completely natural.

Because Esperanto normally states the subject clearly in each clause.

So:

• Se mi pravus ĉiam, mi neniam erarus

has two clauses, and each clause has its own subject:

1. mi pravus
2. mi erarus

Even though it is the same person both times, repeating mi is standard and makes the sentence clear and well-formed.

English does the same thing:

• If I were always right, I would never be wrong

We do not normally say:

• If I were always right, would never be wrong

Esperanto works similarly here.

Yes. That version is also correct.

Compare:

• sed tiel ne estas
• sed ne estas tiel

Both mean essentially the same thing: but that is not the case.

The difference is mostly one of emphasis and style.

• sed tiel ne estas puts a bit more focus on tiel = in that way / like that
• sed ne estas tiel may sound a little more neutral to some speakers

So the sentence you have is fine, and this alternative would also be fine.

Not necessarily.

It only says that the hypothetical situation is not true:

• the speaker is not always right
• therefore, the ideal condition in the first half does not match reality

So sed tiel ne estas does not mean I am always wrong. It only means things are not like that.

In other words:

• I am not always right
• therefore I do sometimes make mistakes

That is a softer and more accurate interpretation.