Learn Hardcore Finnish: Siskoni on niin keskittynyt koripalloon, että unohtaa joskus syödä iltapalaa. - My sister is so focused on basketball that she sometimes forgets to eat an evening snack.

With a possessive suffix
- sisko = sister
- sisko + ni → siskoni = my sister
With a possessive pronoun + noun (+ optional suffix)
- minun siskoni = my sister (literally my my-sister if you also add -ni)

In this sentence, siskoni alone is completely normal and usually preferred in everyday speech.
Minun siskoni is also correct; it just puts more emphasis on my (e.g. contrasting with someone else’s sister).

So:

Siskoni on niin keskittynyt... = perfectly natural, neutral
Minun siskoni on niin keskittynyt... = “My sister (as opposed to others) is so focused...”

What exactly is keskittynyt? Is it a tense like “has concentrated”?

Keskittynyt is the active past participle of the verb keskittyä (to concentrate, to focus).

Dictionary form: keskittyä
Past participle (active): keskittynyt

When you combine this participle with olla (to be), it usually describes a state, not a past action:

hän on keskittynyt = she is focused / she is concentrating (state now)

So Siskoni on niin keskittynyt... is best understood as:

My sister is so focused...

It does not mean my sister has concentrated; instead, the participle behaves like an adjective here, similar to English is focused.

Why is it koripalloon and not just koripallo?

The verb keskittyä (to concentrate, focus) always takes its target in the illative case (the “into / to” case):

keskittyä johonkin = to focus on something

Koripalloon is:

koripallo (basketball) + -on → koripalloon (into/to basketball)

So literally keskittynyt koripalloon means focused into basketball, which corresponds to focused on basketball in English.

If you used plain nominative koripallo, it would be grammatically wrong with keskittyä, because the verb demands that illative -oon / -een / -hVn ending.

Could you use koripallosta instead of koripalloon?

Not with keskittyä.

Different verbs use different cases for their complements:

keskittyä johonkin → illative (-oon / -een):
- keskittyä koripalloon = to focus on basketball
kiinnostua jostakin → elative (-sta / -stä):
- kiinnostua koripallosta = to become interested in basketball

So:

Siskoni on keskittynyt koripalloon = She is focused on basketball.
Siskoni on kiinnostunut koripallosta = She is interested in basketball.

With keskittyä, koripalloon is the only correct choice.

What does the niin … että structure mean here?

Niin … että forms a result/consequence construction:

niin [adjective/adverb] että [clause]
= so [adjective/adverb] that [result]

In this sentence:

niin keskittynyt = so focused
että unohtaa joskus syödä iltapalaa = that she sometimes forgets to eat supper

So the structure is exactly:

Siskoni on niin keskittynyt koripalloon, että unohtaa joskus syödä iltapalaa.
= My sister is so focused on basketball that she sometimes forgets to eat supper.

This use of että is similar to English that in “so … that …”, not the same as just “that” in “I know that she is tired” (though it’s the same word in Finnish).

Why is there a comma before että?

In Finnish punctuation, että usually introduces a subordinate clause, and there is typically a comma before it.

Here:

Main clause: Siskoni on niin keskittynyt koripalloon
Subordinate/result clause: että unohtaa joskus syödä iltapalaa

These are separated by a comma:

..., että unohtaa joskus syödä iltapalaa.

So the comma isn’t optional decoration; it follows a standard rule: a comma before että when it begins a new clause.

Why is the adverb joskus after unohtaa instead of before it? Could you say joskus unohtaa?

Both orders are possible:

unohtaa joskus syödä iltapalaa
joskus unohtaa syödä iltapalaa

Both mean she sometimes forgets to eat supper.

Nuance:

unohtaa joskus (as in the original) is a very neutral, common placement.
joskus unohtaa can put a tiny bit more emphasis on sometimes (e.g. sometimes she forgets, not always), but in everyday speech the difference is very small.

You can also say:

unohtaa syödä iltapalaa joskus

That’s also grammatical, but less common here and can sound a bit heavier or “tagged on” at the end.

So yes, joskus unohtaa syödä iltapalaa would also be correct and natural.

Why is it syödä and not syö or syömään after unohtaa?

After unohtaa (to forget), Finnish uses the 1st infinitive (the dictionary -a/ä form):

unohtaa tehdä = to forget to do
unohtaa syödä = to forget to eat
unohtaa soittaa = to forget to call

So unohtaa syödä is the standard pattern: forgets to eat.

Other forms would change the meaning:

unohtaa syö – incorrect (finite verb syö can’t follow unohtaa like this)
unohtaa syömään – would suggest “forgets to (go) to eat” in a movement sense, and even then you’d normally say unohtaa mennä syömään (“forgets to go eat”).

So the correct and natural construction is:

unohtaa + 1st infinitive → unohtaa syödä.

Why is iltapalaa in the partitive case and not iltapala?

Iltapalaa is the partitive singular of iltapala (evening snack, supper).

With food and drink, syödä / juoda + partitive is very common and usually implies:

an unspecified amount, or
viewing the action as ongoing / incomplete / not about a specific, whole item.

Examples:

Syön omenan. = I eat the apple (a specific whole apple).
Syön omenaa. = I’m eating (some) apple.
Syön iltapalaa. = I eat some supper / I’m having supper.

In this sentence:

syödä iltapalaa ≈ to eat supper / to have an evening snack (not a single clearly bounded “object” the speaker is thinking about).

If you said:

unohtaa syödä iltapalan (genitive), that would sound like forgetting to eat a specific, whole evening snack that is somehow individuated (e.g. the snack that was prepared). That’s possible but more specific and less general than iltapalaa here.

So iltapalaa is partitive because we’re talking about eating some evening food in general, not a clearly delimited “whole object”.

Could you say iltapalansa instead of iltapalaa to mean “her evening snack”?

Yes, but the meaning shifts slightly.

iltapalaa = (some) evening snack / supper in general
iltapalansa = her (own) evening snack, seen as a specific, whole item (genitive + possessive suffix)

Comparing:

unohtaa joskus syödä iltapalaa
= sometimes forgets to eat supper (general habit)
unohtaa joskus syödä iltapalansa
= sometimes forgets to eat her evening snack (you imagine a particular snack that is “hers” and complete)

Both are grammatical; the original sentence just talks about the activity of having supper in general, so iltapalaa is more neutral.

Is siskoni singular or plural? Could it mean “my sisters”?

In this sentence, siskoni is singular:

sisko = sister
siskoni = my sister

However, forms with -ni can sometimes be ambiguous between “my X” (singular) and “my Xs” (plural) depending on the noun, but:

For sisko, the usual plural stem is siskot-, so siskoni is read as singular.
If you needed to be very clear about the plural, you could say siskoni ovat... (my sisters are...), with plural ovat and perhaps a plural form like siskoni (plural) ovat niin keskittyneitä...

Here, the verb is on (3rd person singular), so the grammar clearly indicates one sister: My sister is...

Could you rephrase the sentence with a verb like “to play” instead of the illative koripalloon?

Yes, you could express the same idea slightly differently, for example:

Siskoni on niin keskittynyt pelaamaan koripalloa, että unohtaa joskus syödä iltapalaa.
= My sister is so focused on playing basketball that she sometimes forgets to eat supper.

Changes:

keskittynyt koripalloon → keskittynyt pelaamaan koripalloa
- Now the focus is on the activity of playing basketball rather than on basketball as an interest in general.
- pelaamaan is the illative form of the MA-infinitive of pelata (to play), commonly used after verbs expressing starting, continuing, or focusing on an activity.

Both versions are natural; the original is just a bit more compact.

Is the whole sentence in present tense? How do we know?

Yes, everything is in the present tense or describing a present state:

on = is (3rd person singular present of olla)
keskittynyt = participle describing her current state (is focused)
unohtaa = forgets (3rd person singular present)
syödä = infinitive, “to eat”

So the time frame is:

now / generally → My sister is (currently/typically) so focused on basketball that she sometimes forgets to eat supper.

There is no past-tense verb here like oli (was) or unohti (forgot).