Karena kunci rumah tertinggal di kantor, saya mau tidak mau kembali ke sana.

Karena means because or since.

Yes, it can very naturally come at the beginning of a sentence, just like because in English when you put the reason first:

• Karena kunci rumah tertinggal di kantor, saya ...
• Saya ... karena kunci rumah tertinggal di kantor.

Both are correct. When the karena clause comes first, Indonesian often uses a comma after it, as in this sentence.

In Indonesian, the main noun usually comes first, and the word that describes or specifies it comes after.

So:

• kunci rumah = house key / key to the house
• literally: key house

This is a very common Indonesian pattern:

• mobil polisi = police car
• pintu kantor = office door
• buku pelajaran = textbook

So kunci rumah is the normal word order.

It can mean either one, depending on context.

Indonesian does not usually mark definiteness the way English does with the and a/an. So kunci rumah could mean:

• the house key
• a house key
• my house key, if the context makes that clear

In this sentence, English would most naturally translate it as the house key or my house key, because the speaker is clearly talking about a specific key.

Tertinggal here means something like:

• got left behind
• was accidentally left
• was forgotten somewhere

So kunci rumah tertinggal di kantor means the house key was left behind at the office.

A useful thing to know is that ter- often suggests something that happened unintentionally or as a state/result, rather than a deliberate action.

Compare:

• Saya meninggalkan kunci di kantor. = I left the key at the office.
  (focus on the action)
• Kunci tertinggal di kantor. = The key got left behind at the office.
  (focus on the result/situation, often accidental)

Because the sentence is focusing on the key and the fact that it ended up being left behind, not on the deliberate action of leaving it.

Compare:

• Saya meninggalkan kunci rumah di kantor.
  = I left the house key at the office.
  This sounds more like a straightforward action by me.

• Kunci rumah tertinggal di kantor.
  = The house key was left behind at the office. / I accidentally left the house key at the office.
  This sounds more natural when it was a mistake or an unintended situation.

So tertinggal is a very good choice here.

Di is the preposition for in / at / on a place.

So:

• di kantor = at the office
• di rumah = at home
• di meja = on the table

In this sentence, di kantor tells you the location where the key was left behind.

Yes, literally it looks like want not want, but together it is a fixed expression meaning:

• whether one wants to or not
• like it or not
• have no choice
• must, reluctantly

So:

• saya mau tidak mau kembali ke sana = I had no choice but to go back there

It does not mean “I want not to want” or anything literal like that. You should learn mau tidak mau as an idiom.

Often yes, but the nuance is a little different.

• Saya harus kembali ke sana.
  = I have to go back there.

• Saya mau tidak mau kembali ke sana.
  = I have no choice but to go back there. / Whether I want to or not, I have to go back there.

Harus simply states obligation or necessity.
Mau tidak mau adds the feeling of reluctance or lack of choice.

So they are similar, but mau tidak mau is more expressive here.

Because kembali means to return / go back, while pulang specifically means to go home.

Here, the speaker is going back to the office, not home, so kembali ke sana is the right choice.

Compare:

• Saya pulang. = I’m going home.
• Saya kembali ke kantor. = I’m going back to the office.
• Saya kembali ke sana. = I’m going back there.

So kembali is used because the destination is the office.

Ke sana means to there or, more naturally in English, back there.

In this sentence, it refers to the office mentioned earlier:

• di kantor = at the office
• ke sana = back there, meaning back to the office

Indonesian often avoids repeating the noun when it is already clear from context.

Because once kantor has already been mentioned, Indonesian often uses a place word like sana to avoid repetition.

So instead of saying:

• ... saya mau tidak mau kembali ke kantor

the speaker says:

• ... saya mau tidak mau kembali ke sana

Both are correct.
Using ke sana sounds natural and avoids repeating kantor.

These are common Indonesian location words:

• sini = here, near the speaker
• situ = there, near the listener or not far away
• sana = over there, farther away

In many everyday situations, situ and sana can overlap somewhat, but sana often feels more clearly “there/over there.”

In this sentence, ke sana means back there, referring to the office.

Indonesian often leaves things understood from context rather than marking them as explicitly as English does.

For example:

• di kantor can mean at the office
• ke sana can mean to there / back there

English often needs more explicit wording, but Indonesian can sound perfectly natural with less.

If you wanted to make the office more explicit in some contexts, you might say kantor itu, but it is not necessary here.

Saya is more neutral and polite than aku.

• saya = standard, polite, neutral
• aku = informal, personal, casual

Because this is a general example sentence, saya is the safest and most common choice for learners.

If you said:

• Karena kunci rumah tertinggal di kantor, aku mau tidak mau kembali ke sana.

that would also be correct, but it would sound more casual.

Yes, somewhat.

The sentence begins with the reason, then gives the result:

• Karena kunci rumah tertinggal di kantor, saya mau tidak mau kembali ke sana.

You could also say:

• Saya mau tidak mau kembali ke sana karena kunci rumah tertinggal di kantor.

Both are natural. The first version puts more emphasis on the reason first.

Indonesian word order is often flexible enough to allow this kind of change, especially with clauses joined by karena.

It is mostly neutral standard Indonesian.

Why it sounds neutral:

• karena is standard
• saya is polite/neutral
• kembali is standard
• mau tidak mau is a common idiomatic expression

So this sentence would be fine in normal speech and writing. It is not overly formal, but it is not slangy either.