jeoneun bame keopireul masimyeon jami an oge dwaeyo.

저는 uses the topic particle -는, so it sets up I as the topic of the sentence: As for me...

In this sentence, 저는 sounds natural because the speaker is talking about their general habit or tendency:

• 저는 밤에 커피를 마시면 잠이 안 오게 돼요.
  • As for me, if I drink coffee at night, I end up not being able to sleep.

If you used 제가, it would put more focus on I as the subject, which is possible in some contexts, but 저는 is more natural for a general personal statement.

밤에 means at night.

The particle -에 is often used with time expressions to mean at, on, or in:

• 아침에 = in the morning
• 저녁에 = in the evening
• 밤에 = at night

So 밤에 커피를 마시면 means if/when I drink coffee at night.

마시면 is the -(으)면 conditional form of 마시다 (to drink).

• 마시다 = to drink
• 마시면 = if I drink / when I drink

This grammar is used to express a condition:

• 커피를 마시면 = if I drink coffee

In many everyday sentences, -(으)면 can sound like either if or when, depending on context. Here it suggests a repeated result or tendency:

• When I drink coffee at night, I can’t sleep or
• If I drink coffee at night, I end up not sleeping

Because 커피 is the object of the verb 마시다 (to drink), so it takes the object particle -를.

• 커피를 마시다 = to drink coffee

The particle -가 usually marks the subject, not the direct object, so 커피가 마시면 would be incorrect here.

In Korean, 잠이 오다 is a fixed expression that literally means sleep comes and naturally means to get sleepy / to feel sleep coming / to be able to sleep depending on context.

So:

• 잠이 오다 = sleep comes
• 잠이 안 오다 = sleep doesn’t come

That is why 잠 takes the subject particle -이. Korean expresses this idea differently from English. English says I can’t sleep, but Korean often says sleep doesn’t come.

Literally, 잠이 안 오다 means sleep doesn’t come.

This is a very natural Korean expression. It is commonly used for:

• not being able to fall asleep
• not feeling sleepy
• having trouble sleeping

Examples:

• 잠이 안 와요. = I can’t sleep. / I’m not getting sleepy.
• 어젯밤에 잠이 안 왔어요. = I couldn’t sleep last night.

So even though the literal wording is different from English, it is standard and natural Korean.

안 is the simple negation word meaning not.

Here:

• 오다 = to come
• 안 오다 = to not come

So:

• 잠이 오다 = sleep comes
• 잠이 안 오다 = sleep doesn’t come

This is one of the most common ways to negate a verb in Korean.

-게 되다 often means to come to, to end up, or to become in a certain state or situation.

Here:

• 잠이 안 오다 = sleep doesn’t come
• 잠이 안 오게 되다 = to end up in a state where sleep doesn’t come

So 잠이 안 오게 돼요 has the nuance of:

• I end up not being able to sleep
• It makes it so I can’t sleep
• I wind up unable to sleep

This sounds a little softer and more descriptive than a plain 잠이 안 와요. It suggests a result that happens after drinking coffee at night.

Yes, that would also be natural.

• 잠이 안 와요 = I can’t sleep / sleep doesn’t come
• 잠이 안 오게 돼요 = I end up not being able to sleep

The version with -게 되다 adds a sense of result or becoming that way. It can sound like:

• that’s what happens to me
• that’s the effect it has on me

So both are natural, but the original sentence emphasizes the resulting state a bit more.

The correct form is 돼요.

It comes from:

• 되다
  • -어요
• 되어요 → contracted to 돼요

So:

• 되어요 = correct but less common in speech
• 돼요 = correct and very common
• 되요 = incorrect standard spelling

This is a very common spelling point for learners.

It most naturally sounds like a general tendency or habit.

Because of -(으)면, the sentence suggests:

• Whenever/if I drink coffee at night, this happens

So it sounds like the speaker is saying coffee at night usually causes this result for them.

If you wanted to talk about one specific past event, you would normally use a different form, for example:

• 어젯밤에 커피를 마셔서 잠이 안 왔어요.
  • I drank coffee last night, so I couldn’t sleep.

Yes. Korean often drops subjects and topics when they are understood from context.

So you could simply say:

• 밤에 커피를 마시면 잠이 안 오게 돼요.

This still sounds natural, especially if it is already clear that you are talking about yourself. Korean frequently omits information that English usually keeps.

돼요 is in the polite casual style, also called 해요체. It is appropriate in many everyday situations:

• conversations with people you do not know well
• polite daily speech
• most normal social interactions

It is less formal than 됩니다, but more polite than plain casual speech.

Examples:

• 잠이 안 오게 돼요. = polite everyday style
• 잠이 안 오게 됩니다. = more formal
• 잠이 안 오게 돼. = casual/intimate

Yes. Korean often expresses ideas in ways that do not match English word-for-word.

Instead of saying I sleep / I don’t sleep, Korean often says:

• 잠이 오다 = sleep comes
• 잠이 안 오다 = sleep doesn’t come

This expression focuses on the arrival of sleepiness or sleep rather than the action of sleeping itself. It is one of those very common patterns that learners simply need to get used to.

So although English says I can’t sleep, Korean often naturally says sleep won’t come.