Learn Hardcore Croatian: Na sastanku smo došli do zaključka da je ovaj plan dobar. - At the meeting we came to the conclusion that this plan is good.

The base noun is sastanak = “meeting”.
sastanku is locative singular of sastanak.
The preposition na with the locative often means “at (an event / surface / location)”, so na sastanku = “at the meeting” in the sense of “while the meeting was happening, during the meeting”.

Why is it na sastanku and not u sastanku?

Croatian normally uses:

na
- locative for events and activities:
- na sastanku – at a meeting
- na koncertu – at a concert
- na predavanju – at a lecture
- na poslu – at work
u
- locative for enclosed spaces:
- u sobi – in the room
- u školi – in the school
- u uredu – in the office

A meeting is treated as an event, not as a physical container, so the natural choice is na sastanku, not u sastanku.

What tense is smo došli, and why do we need the separate word smo?

smo došli is the past tense (perfect) of doći = “to come”.

Croatian forms the perfect with:

a present tense of biti (“to be”) as an auxiliary
plus the l-participle of the main verb

So:

mi smo došli = “we came / we have come”
- smo = “we are / we have” (auxiliary, 1st person plural of biti)
- došli = past (l‑)participle of doći, masculine plural form

In everyday speech, this perfect tense is the normal past tense in Croatian.

Why is the word order Na sastanku smo došli? Could it be Na sastanku došli smo or Došli smo na sastanku?

The short verb forms like sam, si, je, smo, ste, su (forms of biti used as auxiliaries) are clitics. They strongly prefer to stand in second position in the clause, after the first stressed word or phrase.

In Na sastanku smo došli…
- Na sastanku is the first phrase, so smo comes right after it (second position).
Na sastanku došli smo… sounds wrong, because the clitic smo has been pushed out of that second position.
If you start with the verb, you can say:
- Došli smo do zaključka… – “We came to the conclusion…”

So the word order is largely dictated by the rule that smo wants to be in second position in the sentence or clause.

What does the phrase doći do zaključka mean exactly?

doći do zaključka is an idiomatic expression meaning “to come to a conclusion” / “to reach a conclusion”.

Literally:

doći – to come
do – to, up to
zaključka – (of) conclusion

So literally: “to come to (the) conclusion.” This structure doći do + genitive is common for “reaching” something (often abstract):

doći do dogovora – to reach an agreement
doći do rješenja – to come to a solution
doći do problema – to get into trouble / problems

Why is it zaključka and not zaključak?

The base form is zaključak = “conclusion” (nominative singular).

After the preposition do, Croatian normally uses the genitive case:

do + genitive

So:

nominative: zaključak
genitive singular: zaključka

That’s why the sentence has do zaključka (“to the conclusion”) instead of do zaključak.

What does da do in da je ovaj plan dobar?

Here da is a conjunction meaning “that”, introducing a subordinate clause which gives the content of the conclusion:

došli smo do zaključka da…
= “we came to the conclusion that…”

So da je ovaj plan dobar = “that this plan is good.”

(Elsewhere, da can also mean “so that / in order to”, but here it’s just “that”.)

Why is there a je in da je ovaj plan dobar? Could we say da ovaj plan dobar?

je is the 3rd person singular present of biti (“to be”).

In Croatian, you generally need this linking verb biti between a subject and an adjective:

ovaj plan je dobar – this plan is good

Inside the da‑clause, the same rule applies:

da je ovaj plan dobar – “that this plan is good”

The version da ovaj plan dobar (without je) sounds incomplete or wrong in normal prose. You may see such omission only in very telegraphic / headline style, not in standard sentences.

Can the word order inside the da‑clause be different, like da ovaj plan je dobar or da je dobar ovaj plan?

da je ovaj plan dobar – neutral, most natural.
da je dobar ovaj plan – also correct; it puts a bit more emphasis on dobar (“good”), like “that good is this plan” → “that this plan is good (as opposed to something else)”.
da ovaj plan je dobar – sounds odd or non‑standard. The clitic verb je again prefers to be in a “second” position after da, so da je ovaj plan dobar is the normal pattern.

So you can move ovaj plan and dobar a bit for emphasis, but the clitic je will usually stay right after da.

What case is ovaj plan, and why?

ovaj plan is in the nominative singular masculine:

ovaj – “this” (masculine nominative singular demonstrative)
plan – “plan” (masculine nominative singular noun)

In the clause ovaj plan je dobar, ovaj plan is the subject, so it appears in nominative. The adjective dobar agrees with plan in gender, number, and case (masculine singular nominative).

Why is it došli and not došao or došle?

The past participle agrees with the person and gender of the subject.

For mi (“we”):

mi smo došli – if the group is all male or mixed (standard default form)
mi smo došle – if the group is all female

Other persons:

ja sam došao – I came (male speaker)
ja sam došla – I came (female speaker)
oni su došli – they came (all male / mixed)
one su došle – they came (all female)

In your sentence, došli assumes either an all‑male or mixed‑gender group.

Could we replace smo došli do zaključka with smo zaključili? Is there any difference?

Yes, you can say:

Na sastanku smo zaključili da je ovaj plan dobar.

This also means: “At the meeting we concluded that this plan is good.”

Difference in nuance:

doći do zaključka – literally “to come to a conclusion”; slightly more idiomatic / descriptive, like reaching that point.
zaključiti – “to conclude, to decide”; more direct and compact.

In most contexts, they are interchangeable in meaning.

Does ovaj plan mean “the plan” or “a plan” in English?

Croatian has no articles (“a/an/the”), so it uses other means:

ovaj plan literally = “this plan”.
Depending on context, in English you might translate it as:
- “this plan” (if contrast is important)
- or naturally as “the plan” (if it’s already clear which plan you’re talking about)

It does not usually mean just “a plan” in a vague, indefinite sense; it points to a specific plan that is already known in the situation.