Learn Hardcore Indonesian: Kadang-kadang kami gagal, tetapi kami belajar banyak.

kami = we (excluding the listener). Use this when the person you’re talking to is not part of the group.
kita = we (including the listener). Use this when the listener is part of the group. In the sentence, kami is correct if you’re talking to someone outside your group. If the listener is included, say Kadang-kadang kita gagal, tetapi kita belajar banyak.

Do I have to repeat kami after tetapi, or can I drop it?

You can drop it if the subject is obvious from context: Kadang-kadang kami gagal, tetapi belajar banyak. Repeating kami is also natural and adds clarity. Both are fine; repetition is common in careful or formal writing.

Can I use tapi instead of tetapi?

Yes. tapi is more casual; tetapi is neutral-formal. You can also use:

namun (often at the start of the clause): Kadang-kadang kami gagal; namun, kami belajar banyak.
akan tetapi (formal): Kadang-kadang kami gagal, akan tetapi kami belajar banyak.

Why is there a comma before tetapi?

Indonesian typically uses a comma before coordinating conjunctions (like tetapi, melainkan, sedangkan) that link two independent clauses. So ..., tetapi ... is standard punctuation.

Does kadang-kadang have to be hyphenated? Are there alternatives?

Standard spelling uses a hyphen: kadang-kadang. Alternatives:

terkadang (one word, common in writing)
kadang kala (two words) or kadangkala (one word)
sesekali (less frequent than kadang-kadang; “once in a while”)

Where can I place kadang-kadang in the sentence?

All are acceptable, with slightly different emphasis:

Kadang-kadang kami gagal, ... (fronted adverb, common)
Kami kadang-kadang gagal, ... (after subject, very natural)
Kami gagal kadang-kadang, ... (possible but less common) Choose the first two for most contexts.

Is gagal a verb or an adjective? How do I use it with specific contexts like exams?

gagal functions like an intransitive verb or stative adjective meaning “to fail/unsuccessful.”

General: Kami gagal.
With a context: Kami gagal dalam ujian (we failed the exam), Kami gagal mencapai target (we failed to reach the target). Avoid gagal untuk + verb in everyday style; prefer gagal + verb or gagal dalam + noun.

How do I show past vs habitual time here, since Indonesian has no tense?

Use time words or aspect markers:

Past specific: Kami tadi gagal, Kami kemarin gagal.
Experience: Kami pernah gagal.
Completed: Kami sudah gagal (we have already failed).
Habitual (fits the original): Kadang-kadang kami gagal (we sometimes fail).

Is belajar banyak the same as banyak belajar?

belajar banyak = learn a lot (of things/lessons). You can make it explicit: belajar banyak hal.
banyak belajar = study a lot (time/effort/frequency). Both are correct; pick based on what you want to emphasize.

Can belajar take a direct object, or must I use mempelajari?

belajar can take an object: belajar Bahasa Indonesia, belajar matematika. It’s general and common.
mempelajari is more formal and clearly transitive, focusing on the object: Kami mempelajari struktur bahasa. In the original sentence, belajar is perfect.

Pronunciation tips for key words?

kadang-kadang: kah-dahng-kah-dahng (final ng = [ŋ], as in “sing”)
tetapi: tuh-TAH-pee (clear “t” sounds)
belajar: buh-LA-jar (“j” like English “j”; tapped/flapped Indonesian r)
banyak: BAH-nyak (ny = [ɲ], like Spanish ñ in “niño”) Stress is light; Indonesian is syllable-timed.

What’s the difference between kadang-kadang and sering?

kadang-kadang = sometimes (occasional)
sering = often/frequently So Kadang-kadang kami gagal < less frequent than Kami sering gagal.

Is kalah the same as gagal?

Not exactly:

kalah = to lose (against an opponent): Kami kalah 2–1.
gagal = to fail (not achieve a goal): Kami gagal mencapai target. In many contexts they’re not interchangeable.

How can I make the sentence more formal or more casual?

More casual: Kadang kami gagal, tapi kami banyak belajar.
More formal: Adakalanya kami mengalami kegagalan; namun, kami memperoleh banyak pembelajaran.

Why is belajar formed with bel- instead of ber-?

It’s an irregular allomorph: bel- is a special form of ber- that appears almost exclusively with the root ajar to form belajar. It’s a set phrase you simply memorize.