sore ha kouun desita.

は is the topic marker. It tells you what the sentence is about.

So here:

• それ = that
• は = as for / speaking of
• 幸運でした = was fortunate / was good luck

A very literal way to feel the structure is:

• As for that, it was fortunate.

In natural English, we usually just say That was lucky or That was fortunate.

Also, remember that は is written ha but pronounced wa when it is a particle.

Yes. でした is the polite past form of です.

• です = is / am / are
• でした = was / were

So:

• 幸運です = is fortunate / is good luck
• 幸運でした = was fortunate / was good luck

Japanese does not change for singular/plural the way English does, so the same でした can correspond to was or were, depending on context.

In this sentence, 幸運 is functioning like a noun predicate with でした.

幸運 basically means good fortune, luck, or good luck. So the sentence can feel like:

• That was good fortune
• That was fortunate
• That was lucky

Japanese often uses nouns in places where English might prefer an adjective.

You may also see 幸運な before a noun:

• 幸運な人 = a fortunate person

So it is useful to think of 幸運 as a word that can behave like a noun and also like a na-adjective-type word depending on the structure.

These words depend on distance and context:

• これ = this (near the speaker)
• それ = that (near the listener, or something just mentioned)
• あれ = that over there (away from both)

In many conversations, それ is also used for something the other person just said or something already mentioned.

So それは幸運でした could mean:

• That was lucky
• referring to some event or fact already under discussion

If the speaker were talking about something physically near them, これは幸運でした would be possible. If it were distant from both people, あれは幸運でした might fit better.

No. Japanese is normally written without spaces.

So the normal writing is:

• それは幸運でした。

Learner materials often add spaces to make the parts easier to see:

• それ / は / 幸運 / でした

That is just for study purposes.

It is polite because it uses でした.

Politeness comparison:

• それは幸運でした。 = polite
• それは幸運だった。 = casual/plain

So you would normally use でした in:

• polite conversation
• talking to someone you do not know well
• customer service, school, workplace, etc.

You would use だった with friends, family, or in casual narration.

Yes, often you can.

Japanese often omits things that are obvious from context. So if everyone already knows what you are talking about, you can simply say:

• 幸運でした。

That would mean something like:

• It was fortunate.
• That was lucky.

Adding それは makes the topic explicit and can give a slight feeling of contrast or emphasis, like As for that, it was fortunate.

Yes, it is understandable and natural enough, especially in polite speech, but it sounds a bit formal or bookish because of 幸運.

More conversational alternatives include:

• それは運がよかったです。 = That was lucky.
• それはラッキーでした。 = That was lucky.

Nuance:

• 幸運でした = somewhat formal, abstract, elegant
• 運がよかったです = very natural, common
• ラッキーでした = casual-feeling, modern, conversational

So それは幸運でした is fine, but it may sound more elevated than everyday speech.

This is a very common confusion.

• 幸運 = good luck / fortunate circumstance / good fortune
• 幸せ = happiness

So:

• それは幸運でした。 = That was lucky / fortunate.
• それは幸せでした。 would sound more like That was happiness or That made me happy, depending on context, and is much less natural in that exact form.

In short:

• 幸運 is about luck
• 幸せ is about feeling happy or being happy

Because 幸運 is the predicate here, not the subject.

Structure:

• それは = topic
• 幸運でした = predicate

This is like saying:

• X was Y

where Y is 幸運.

You would use が in different structures, for example:

• 運がよかったです。 = Luck was good / I was lucky.

There, 運 is the thing marked by が. But in それは幸運でした, 幸運 is simply what それ is being identified as.

It is pronounced:

• so-re-wa

Even though the particle is written は, when it marks the topic it is pronounced wa.

So the whole sentence is pronounced roughly:

• so-re wa koo-un de-shi-ta

A few notes:

• 幸運 is こううん
• the うう is not two strongly separated syllables in English style; it makes a long oo-like sound
• でした is pronounced clearly as de-shi-ta

Not directly by itself in normal grammar. If 幸運 is modifying a noun, you usually use な:

• 幸運な出来事 = a fortunate event
• 幸運な人 = a lucky person

But when it is the main predicate of the sentence, you can say:

• それは幸運でした。

So:

• before a noun: 幸運な
• at the end with polite copula: 幸運です / 幸運でした

Yes. That depends on how you interpret 幸運 in context.

Because 幸運 is basically a noun meaning good fortune or good luck, the sentence can feel like:

• That was good luck
• That was fortunate

English chooses between a noun-style translation and an adjective-style translation depending on what sounds natural in context.

So both kinds of meaning are built into the Japanese, and context decides which English wording is best.