kouun datta node, seikousimasita.

幸運 is basically a noun meaning good luck or fortune, but it can also behave like a na-adjective in some contexts.

In this sentence, it is being used as the predicate of the clause, so it needs a form of だ:

• 幸運だ = is fortunate / is good luck
• 幸運だった = was fortunate / was good luck

So even though 幸運 is a noun, Japanese often lets nouns and na-adjectives work this way with だ.

だった is the past plain form of だ.

So:

• 幸運だ = is fortunate
• 幸運だった = was fortunate

Because the sentence is talking about a completed situation that led to success, the speaker uses the past form.

Here, ので attaches to the plain form before it, so:

• 幸運だったので = because it was fortunate / because I was lucky

Using 幸運で would be a different structure. It can connect ideas too, but 幸運だったので more clearly gives a reason/cause.

This is very common in Japanese.

In subordinate clauses, Japanese often uses the plain form, even when the main clause is polite:

• 幸運だったので、成功しました。

This is completely natural.

You can think of it like:

• subordinate reason clause: plain
• main statement: polite

A more fully polite version such as 幸運でしたので、成功しました is possible, but it sounds more formal or stiff. In everyday Japanese, だったので + polite ending is very normal.

ので means because, since, or so. It gives a reason for what happens in the main clause.

So the structure is:

• 幸運だったので = because I was lucky / because it was good fortune
• 成功しました = (I/they) succeeded

Compared with から, ので often sounds a little softer, more explanatory, and sometimes more objective.

For example:

• 幸運だったので、成功しました。 = Because I was lucky, I succeeded.
• 幸運だったから、成功しました。 = I succeeded because I was lucky.

Both are correct, but ので can sound slightly more neutral or less blunt.

成功しました is the polite past form of 成功する.

• 成功する = to succeed
• 成功しました = succeeded / was successful

The sentence describes something that already happened:

• first, there was good luck
• as a result, success happened

So the past tense is natural.

If you changed it to 成功します, it would usually sound like a future or habitual statement, which would not fit this sentence as well.

Japanese often leaves out the subject when it is understood from context.

So 幸運だったので、成功しました。 could mean:

• I was lucky, so I succeeded.
• He/She was lucky, so he/she succeeded.
• We/They were lucky, so we/they succeeded.

The sentence by itself does not tell you exactly who the subject is. You have to get that from the surrounding context.

This is one of the most common features of Japanese, and it can feel strange to English speakers at first.

It can suggest either one depending on context.

Japanese is often less explicit than English about exactly how to phrase this idea. 幸運だった can be understood as:

• I was fortunate
• it was good luck
• the situation was fortunate

In natural English, people often translate it as because I was lucky if the subject is a person.

So grammatically the Japanese is a little broader, but in normal use the intended meaning is usually easy to understand from context.

Yes, it is understandable and grammatical. However, depending on the situation, many speakers might more naturally say something like:

• 運が良かったので、成功しました。

This literally means because my luck was good, I succeeded, and it is a very common way to express the idea.

That said, 幸運だったので、成功しました is still valid. It can sound a bit more formal, literary, or abstract than 運が良かったので.

So:

• 幸運だったので = correct, somewhat formal/bookish
• 運が良かったので = very common and conversational

Good question. They are related, but not identical.

• 成功しました = succeeded
• 成功できました = was able to succeed / managed to succeed

成功しました simply states the result.

成功できました puts more focus on the fact that success was possible or achieved despite difficulty.

In your sentence, 成功しました is the more straightforward and natural choice.

The comma helps separate the reason clause from the main clause:

• 幸運だったので、成功しました。

It makes the sentence easier to read, especially when the first part gives background or explanation.

In Japanese, punctuation is somewhat flexible, so you may also see sentences without a comma. But with a clause ending in ので, a comma is very common and natural.

No. In normal Japanese writing, you would usually write it without spaces:

幸運だったので、成功しました。

Spaces are often added only in beginner materials to make the sentence easier to read. Real Japanese text normally does not separate words with spaces.

A natural reading is:

こううん だった ので、せいこう しました。

In romaji:

kōun datta node, seikō shimashita

A few pronunciation notes:

• 幸運 = こううん
• 成功 = せいこう
• long vowels matter in both words: kōun, seikō

So if you are reading it aloud, try not to shorten those long ō sounds.