Learn Hardcore Croatian: Ponekad ne znamo kako iskoristiti priliku koja se dogodi samo jednom. - Sometimes we do not know how to make use of an opportunity that happens only once.

Ponekad – sometimes
ne znamo – we don’t know
- ne – not
- znamo – we know (1st person plural, present)
kako – how
iskoristiti – to make use of / to take advantage of (perfective infinitive)
priliku – (the) opportunity (accusative singular of prilika)
koja – which / that (feminine singular relative pronoun, referring to prilika)
se – reflexive clitic (here more grammatical than truly “reflexive”)
dogodi – happens / occurs (3rd person singular, perfective)
samo – only
jednom – once (literally: “one time”)

So literally:
“Sometimes we don’t know how to use the opportunity which happens only once.”

Why is it priliku and not prilika?

Prilika is a feminine noun:

Nominative singular: prilika (subject form)
Accusative singular: priliku (direct object form for most feminine -a nouns)

In the sentence, priliku is the direct object of the verb iskoristiti (“to use / take advantage of”):

iskoristiti (što?) priliku – to use what? → the opportunity

Because it is a direct object, you must use the accusative, so:

prilika → subject:
- Prilika je važna. – The opportunity is important.
priliku → object:
- Iskoristi priliku. – Use the opportunity.

Hence, kako iskoristiti priliku is grammatically correct, not kako iskoristiti prilika.

Why is there ne znamo and not something like a double negative (e.g. ne znamo ništa kako …)?

Croatian uses double negatives with negative pronouns/adverbs (e.g. nitko, ništa, nikad, nigdje), but the verb itself only gets one “ne”.

For example:

Ne znamo ništa. – We don’t know anything. (literally “We don’t know nothing.”)
Ne znam nikoga. – I don’t know anyone. (“I don’t know nobody.”)

In your sentence, there is no negative pronoun, just a clause with kako (“how”):

Ne znamo kako iskoristiti priliku… – We don’t know how to use the opportunity…

So you only negate the verb znamo with ne. There is no need (and no place) for a second negative here.

Why is it kako iskoristiti and not kako iskoristimo?

Both structures are possible in Croatian, but they have slightly different grammar and style:

kako + infinitive
- kako iskoristiti priliku – how (to) use the opportunity
  This is similar to English “how to use”.
  After kako, using the infinitive is quite natural and neutral in Croatian.
kako da + finite verb
- kako da iskoristimo priliku – how we should use / how to (go about) using the opportunity
  This is also correct and sounds a bit more “verbal”, a bit more like “how we should / could do it”.

In your sentence, kako iskoristiti priliku is:

grammatically correct,
idiomatic,
slightly more neutral and compact.

So ne znamo kako iskoristiti priliku ≈ “we don’t know how to use the opportunity”, and you don’t need da or a conjugated verb here.

What is the difference between iskoristiti and koristiti?

Both are related to the idea of “use”, but:

koristiti – to use (imperfective)
- Focus on the ongoing / habitual action.
- Example: Znam kako koristiti ovaj program. – I know how to use this program.
iskoristiti – to make (full) use of, to take advantage of (perfective)
- Focus on a single, completed use, often with the nuance of using fully / taking the chance.
- Example: Moramo iskoristiti ovu priliku. – We must take advantage of this opportunity.

In the sentence iskoristiti priliku koja se dogodi samo jednom, the idea is clearly a unique opportunity you should fully take advantage of once it appears, so the perfective verb iskoristiti is the natural choice.

Why do we use dogodi and not događa?

This is an aspect choice:

događati se – to happen (imperfective): used for ongoing, repeated, habitual happenings.
dogoditi se – to happen (perfective): used for a single, completed event.

In the sentence:

priliku koja se dogodi samo jednom
literally: “the opportunity which happens only once”

Because we are talking about an opportunity that happens only once, we want one single event, which is why we use the perfective:

dogodi (se) – “(that) happens (once)”

If you said koja se događa samo jednom, it would sound less natural, because događa se suggests something that may repeat or have duration, which clashes slightly with samo jednom (“only once”).

What is the function of se in koja se dogodi and why is it placed there?

Dogoditi se is a reflexive / pronominal verb in Croatian:

basic form: dogoditi se – to happen, to occur
in a sentence: nešto se dogodi – something happens

So se is the reflexive pronoun that is part of the verb.

As for the position: Croatian has a rule that clitics (short unstressed words like se, je, sam, mi, ga, etc.) tend to appear in second position in the clause.

In the relative clause:

koja se dogodi
- koja – “which/that” (the first word in the clause)
- se – clitic, placed second
- dogodi – the main verb

You could say koja dogodi se in very informal speech, but it sounds off/incorrect in standard Croatian.
Standard word order for this type of clause is koja se dogodi.

Why is the relative pronoun koja used, and not što?

Both koja and što can introduce relative clauses, but they are not used in the same way.

Koja (from koji, koja, koje) is a proper relative pronoun and agrees in gender, number, and case with the noun it refers to.
- Noun: prilika – feminine singular
- So: koja – feminine singular nominative
- prilika koja se dogodi… – the opportunity that happens…
Što is more like “what/that” and often used in different structures, especially after demonstratives or for more general ideas:
- Ono što kažeš je točno. – What you say is correct.
- Sve što znam… – All that I know…

When you directly modify a specific noun like prilika, standard Croatian prefers koji/koja/koje:

prilika koja se dogodi samo jednom – the opportunity that happens only once

Using što here would sound non‑standard or dialectal in many contexts.

What exactly does samo jednom mean, and is it a special form?

Samo jednom literally means “only once”.

samo – only, just
jednom – once (literally “one time”)

Jednom is the instrumental or locative form of “jedan” (“one”), but here it is functioning as a frozen adverbial expression meaning “once”. You don’t need to worry about its case here; just treat jednom after verbs like dogoditi se as “once”:

To se dogodilo jednom. – That happened once.
Samo jednom u životu. – Only once in a lifetime.

You can also say:

samo jedanput – also “only once”, a bit more explicit but fully correct.

Can we move samo jednom in the sentence, for example: … priliku koja se samo jednom dogodi?

Yes. Croatian word order is relatively flexible, especially with adverbs.

Both are possible and natural:

priliku koja se dogodi samo jednom
priliku koja se samo jednom dogodi

Differences:

…dogodi samo jednom
- Slightly neutral: focusing a bit more on the frequency of the action (“happens only once”).
…samo jednom dogodi
- Slight emphasis on “only once” in front of the verb, but in everyday speech the difference is minimal.

Both versions are correct and idiomatic. Your original sentence uses a very common, natural order.

Could we say Ponekad ne znamo kako da iskoristimo priliku…? Is that correct, and what’s the difference?

Yes, it is correct:

Ponekad ne znamo kako iskoristiti priliku…
Ponekad ne znamo kako da iskoristimo priliku…

Both mean roughly: “Sometimes we don’t know how to use/take the opportunity…”

Nuance:

kako + infinitive (kako iskoristiti)
- Slightly more neutral, more “dictionary-style” or formal.
- Very common in written language.
kako da + finite verb (kako da iskoristimo)
- Feels a bit more conversational; often carries a nuance of “how we are supposed to / how we should do it”.

In many contexts, speakers use them interchangeably, and in your sentence both are fine. The version with the infinitive (your original) is maybe a touch more neutral.

Could we drop the relative clause and just say …kako iskoristiti priliku samo jednom? Would that change the meaning?

If you say:

Ponekad ne znamo kako iskoristiti priliku samo jednom.

it becomes ambiguous and sounds odd, because now samo jednom seems to modify “iskoristiti priliku” (to use the opportunity only once), not “priliku koja se dogodi samo jednom” (an opportunity that only happens once).

Original meaning:

priliku koja se dogodi samo jednom
– “the opportunity that occurs only once”

Changed version:

kako iskoristiti priliku samo jednom
– “how to use the opportunity only once” (as opposed to using it several times)

This slightly changes the focus and is less natural for the intended idea.
So: grammatically possible, but not a good rewrite if you want to keep the original meaning about a once‑in‑a‑lifetime opportunity.

Is there any nuance in ponekad compared to other words for “sometimes,” like katkad?

Both ponekad and katkad mean “sometimes” and are largely interchangeable:

Ponekad ne znamo…
Katkad ne znamo…

Differences:

ponekad is more common in everyday modern speech.
katkad can sound a bit more literary or formal, depending on the region and context, but it is still used in normal conversation too.

In most contexts, especially spoken Croatian, ponekad is the default choice, and that’s why it appears in your sentence.