oneureun uni eobseoseo ipjanggwoneul mos sasseo.

-은/는 is the topic particle. In 오늘은, it marks today as the topic, with a slight sense of as for today or today, at least.

So 오늘은 운이 없어서... can feel a bit like:

• As for today, I had bad luck, so...
• Today, I was unlucky, so...

Using 오늘이 instead would sound different, because -이/가 marks the grammatical subject rather than the topic.

In the expression 운이 없다, 운 is treated as the subject of 없다, so -이/가 is natural.

• 운이 없다 = to have no luck / to be unlucky

This is a very common fixed expression.
Using 운은 없다 is possible in some contrastive contexts, but it is not the default form here.

For example:

• 실력은 있는데 운은 없어. = He has skill, but he has no luck.

In your sentence, 운이 없어서 is the normal, natural choice.

Yes, literally it is something like luck does not exist or there is no luck, but in natural English it means:

• to be unlucky
• to have bad luck

So 운이 없어서 means because I was unlucky or because I had bad luck.

This is a very common Korean way to talk about luck:

• 운이 좋다 = to be lucky
• 운이 나쁘다 = to be unlucky / luck is bad
• 운이 없다 = to have no luck / be unlucky

-아서/어서 connects two clauses and usually means because, so, or sometimes just links actions smoothly.

Here:

• 운이 없어서 = because I was unlucky
• 입장권을 못 샀어 = I couldn’t buy the admission ticket

So the sentence structure is:

• Reason + -아서/어서 + result

In this sentence, 없다 becomes 없어서.

This is a very common pattern:

• 바빠서 못 갔어. = I was busy, so I couldn’t go.
• 돈이 없어서 못 샀어. = I had no money, so I couldn’t buy it.

This is an important difference.

• 안 샀어 = I didn’t buy it
• 못 샀어 = I couldn’t buy it

So:

• 안 usually means you did not do something
• 못 usually means you were unable to do something

In your sentence, the speaker is explaining that bad luck prevented them from buying the ticket, so 못 샀어 is the correct choice.

The verb is 사다 = to buy.

Its past tense is formed like this:

• 사다
• stem: 사-
• past marker: -았-
• casual ending: -어
• 사 + 았 + 어 → 샀어

So:

• 사
  • 았어 becomes 샀어

This is a very common contraction in Korean.

Other examples:

• 가다 → 갔어
• 보다 → 봤어

입장권 means an admission ticket or entry ticket. It is a more specific and formal word than 표.

• 입장권 = ticket for entering a place
• 표 = ticket in general

So if you are talking about a ticket to enter a museum, concert venue, exhibition, or amusement park, 입장권 works well.

Examples:

• 영화표 = movie ticket
• 비행기표 = plane ticket
• 입장권 = admission ticket

In daily speech, Koreans may sometimes use 표 more casually, depending on context.

Yes. 샀어 is an informal, casual ending, often used with:

• friends
• family
• people younger than you
• diary-style speech
• casual conversation

The polite version would be:

• 오늘은 운이 없어서 입장권을 못 샀어요.

And a more formal written or formal spoken style might be:

• 오늘은 운이 없어서 입장권을 못 샀습니다.

So the sentence you gave is in casual speech.

Korean often omits subjects when they are understood from context.

In this sentence, the implied subject is usually I:

• 오늘은 운이 없어서 입장권을 못 샀어.
• Today, I was unlucky, so I couldn’t buy the admission ticket.

Korean does this very often. If the subject is obvious, it is usually left out.

You could add it if needed:

• 나는 오늘은 운이 없어서 입장권을 못 샀어.

But that often sounds unnecessary unless you want emphasis or contrast.

입장권 is the object of 사다 because it is the thing being bought.

• 입장권을 사다 = to buy an admission ticket

The object particle is:

• -을 after a consonant
• -를 after a vowel

Since 입장권 ends in a consonant, it takes -을:

• 입장권 + 을 → 입장권을

Yes, definitely.

• 운이 없어서 = because I had no luck / because I was unlucky
• 운이 안 좋아서 = because my luck wasn’t good

Both are natural.
운이 없어서 can feel a little stronger or more idiomatic, while 운이 안 좋아서 sounds a bit more straightforward and conversational.

So these are both fine:

• 오늘은 운이 없어서 입장권을 못 샀어.
• 오늘은 운이 안 좋아서 입장권을 못 샀어.

Yes, to some extent. Korean word order is flexible, especially as long as the verb stays at the end and particles make the roles clear.

Original:

• 오늘은 운이 없어서 입장권을 못 샀어.

You could also say:

• 오늘은 입장권을 운이 없어서 못 샀어.

But this version is less natural. The original flows better because the reason clause comes first, then the result.

So while Korean allows some movement, the original order is the most natural and easiest to understand.

It can do both.

At the basic level, 오늘은 just sets the time topic: today.

But -은/는 often adds a subtle contrastive feeling. Depending on context, it can suggest something like:

• today, at least
• today though
• as for today

So it might imply:

• maybe other days were different
• today happened to be unlucky
• today specifically, things did not work out

This contrast is often very light and depends on context and intonation.

It usually suggests a specific situation in the past.

Because of 샀어 in the past tense, it sounds like the speaker tried or intended to buy the ticket today, but due to bad luck, it did not happen.

So the feeling is more like:

• I couldn’t buy the ticket today rather than
• I am generally unable to buy tickets

The sentence points to a particular event that already happened.