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bimilbeonhoreul kkamppakhaeseo rogeu-in mos haesseoyo.

비밀번호를 깜빡해서 로그인 못 했어요.bimilbeonhoreul kkamppakhaeseo rogeu-in mos haesseoyo.
I forgot the password, so I couldn’t log in.
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Questions & Answers about bimilbeonhoreul kkamppakhaeseo rogeu-in mos haesseoyo.

What does -를 in 비밀번호를 do?

-를 is the object marker. It marks 비밀번호 (password) as the direct object of the verb 깜빡하다 (to forget momentarily).
So 비밀번호를 깜빡해서 = (I) forgot the password, so…

Why is the subject I not written anywhere?

Korean often omits the subject when it’s obvious from context. In a normal conversation, it’s clear that you are talking about your own login attempt, so 저는/제가 is unnecessary.
If you want to add it for clarity:

  • 제가 비밀번호를 깜빡해서 로그인 못 했어요.
What does 깜빡하다 mean exactly, and how is it different from 잊어버리다?

깜빡하다 means to forget briefly / absentmindedly (a momentary slip). It often sounds casual and very common in speech.
잊어버리다 is a more general to forget (completely) and can feel a bit heavier/stronger.

Examples:

  • 비밀번호를 깜빡했어요. (I blanked on it / forgot it for a moment.)
  • 비밀번호를 잊어버렸어요. (I forgot it.)
What does -아서/어서 (here: -해서) mean in this sentence?

-아서/어서 links two clauses and often means because/so, showing a reason and a result.

Structure:

  • A-아서/어서 B = Because A, (so) B

Here:

  • 비밀번호를 깜빡해서 (because I forgot the password)
  • 로그인 못 했어요 (I couldn’t log in)
Why is it 깜빡해서 and not 깜빡했어서?

In Korean, you usually don’t need to mark past tense in the first (reason) clause if the time is already clear from the main clause. The past meaning is understood from 못 했어요 (past).

Natural:

  • 깜빡해서 못 했어요.

Possible but heavier/less common:

  • 깜빡했어서 못 했어요. (can sound redundant or overly explicit)
How does 못 했어요 work? Is it just “didn’t”?

못 했어요 means couldn’t do (it) due to inability or circumstances, not just a simple choice.

Compare:

  • 로그인 못 했어요. = I couldn’t log in (something prevented it).
  • 로그인 안 했어요. = I didn’t log in (I chose not to / didn’t do it).

In this sentence, forgetting the password naturally leads to 못 했어요.

Why is it 로그인 못 했어요 without 을/를?

With 못 하다, Korean often uses a “short form” where the object marker is omitted in casual speech, especially with common actions like logging in.

More explicit / more “complete” forms:

  • 로그인을 못 했어요.
  • 로그인하지 못했어요. (more formal/neutral; uses -지 못하다)

All are correct; the original is very natural conversational Korean.

What’s the difference between 못 했어요 and -지 못했어요?

They are very similar in meaning (couldn’t), but style differs:

  • 못 했어요: shorter, more conversational.
  • -지 못했어요: a bit more formal/neutral, and can sound slightly more “careful” or explicit.

Examples:

  • 로그인 못 했어요. (casual, very common)
  • 로그인하지 못했어요. (more formal/standard)
Why is there a space in 못 했어요? Should it be one word?

Spacing rules treat 못 (adverb) as separate from the verb:

  • 못 했어요 (standard spacing)

But 못하다 can also be a verb meaning to be bad at:

  • 저는 수영을 못해요. (I’m not good at swimming.)
    In that meaning, it’s often written together (못해요) because it behaves like a single verb.

In your sentence, it’s the “can’t” adverb meaning → 못 했어요.

What level of politeness is 했어요, and what are alternatives?

-했어요 is polite informal (the common everyday polite style).

Alternatives:

  • Casual (to friends): 못 했어.
  • More formal: 못 했습니다. / 로그인하지 못했습니다.
  • Softer/explanatory ending: 못 했어요(요). / 못 했거든요. (adds “you see / because…” nuance)
Is 로그인 the only word for “log in”? Can I say it differently?

로그인 is the most common everyday term (a loanword).

Other options:

  • 접속 (connecting/accessing; more general, sometimes used for “log in” depending on context)
  • 로그인하다 / 로그인되다 (to log in / to be logged in)

Examples:

  • 로그인했어요. (I logged in.)
  • 로그인이 안 돼요. (Login isn’t working / I can’t log in.)
Can I move parts around, like putting the result first?

Yes. Korean is flexible, and you can reorder for emphasis:

Original (reason → result):

  • 비밀번호를 깜빡해서 로그인 못 했어요.

Result first (emphasis on inability):

  • 로그인 못 했어요. 비밀번호를 깜빡해서요.
    The -요 after 해서요 makes it sound like a natural spoken explanation: …because I forgot the password.