Learn Hardcore Finnish: Kun saan vaikean tehtävän valmiiksi, tunnen oloni itsevarmaksi. - When I finish a difficult task, I feel self-confident.

Finnish does not invert subject and verb after kun like English often does after some conjunctions.
So you simply have: kun + subject + verb + rest
- kun
  - saan (I get) + vaikean tehtävän valmiiksi (the difficult task finished)

The comma separates the kun‑clause (subordinate clause) from the main clause, which is standard in writing.

Why is it “saan … valmiiksi” and not just a single verb like lopetan or valmistun?

Saada X valmiiksi is a very common Finnish expression meaning “to get X finished / to complete X.”

saan = I get (from saada, “to get, to receive, to be allowed to”)
valmiiksi = into a finished/ready state (see more on the ending below)

So literally: “When I get a difficult task into a finished state, I feel confident.”
Natural English: “When I finish a difficult task, I feel confident.”

You could use other verbs:

Kun lopetan vaikean tehtävän, … – When I stop/finish a difficult task, …
Kun suoritan vaikean tehtävän, … – When I complete a difficult task, …

…but saada tehtävä valmiiksi is idiomatic, neutral, and very common.

Why is it “vaikean tehtävän” and not “vaikea tehtävä” or “vaikeaa tehtävää”?

Vaikean tehtävän is in the genitive/accusative form, which here marks a total object—an object that is fully completed/affected.

tehtävä = task (nominative)
tehtävän = task (genitive/accusative singular)
vaikea tehtävä = a difficult task (nominative)
vaikean tehtävän = the difficult task as a complete object

Why “total object” here?

The phrase saada tehtävä valmiiksi implies you finish the task completely.
For a fully completed, bounded event, Finnish typically uses the genitive/accusative for the object.

If you talked about doing an indefinite amount of something, or something not completely done, you’d often see the partitive, e.g.:

Teen vaikeaa tehtävää. – I am working on a difficult task. (not necessarily finishing it)

Why does vaikean also end in -n?

In Finnish, adjectives usually agree with the noun in:

case
number
(and sometimes) possessive suffix

Here:

tehtävän is in the genitive/accusative singular.
The adjective vaikea must match that, so it becomes vaikean.

So:

nominative: vaikea tehtävä – a difficult task
genitive/accusative: vaikean tehtävän – (the) difficult task (as a total object)

What exactly is valmiiksi, and why does it end in -ksi?

Valmiiksi is the translative case form of valmis (ready, finished).

valmis → valmiiksi (translative singular)

The translative (-ksi) often expresses a change into a new state or result:

maalata seinä valkoiseksi – to paint the wall white
kääntää tekstin englanniksi – to translate the text into English
leipoa taikina leiväksi – to bake the dough into bread

So saada tehtävä valmiiksi literally is:

to get the task into a ready/finished state.

That’s why valmiiksi is used: the task changes into the state of being finished.

What does “tunnen oloni” literally mean, and why not just say “tunnen itseni”?

Literally:

tunnen = I feel / I sense (from tuntea)
olo = feeling, condition, state (how you feel physically/mentally)
oloni = my feeling/state (see the -ni below)

So tunnen oloni itsevarmaksi = “I feel my state/condition to be confident.”

You can also say:

tunnen itseni itsevarmaksi – I feel (myself) confident.

Both are correct, but:

tuntea olonsa joksikin (to feel one’s state as something) is a very natural fixed pattern.
tuntea itsensä joksikin is also fine, maybe a bit more literally “I feel myself (to be) X.”

Another very common alternative pattern is:

Minusta tuntuu itsevarmalta. – It feels (to me) confident / I feel confident.

All three are understandable; the sentence given uses one of the most idiomatic patterns.

What does the -ni in oloni mean?

The -ni ending is a possessive suffix meaning “my.”

olo = (a) feeling, condition, state
oloni = my feeling/state

So:

minun oloni and oloni both mean “my condition / the way I feel”.
The explicit minun is often left out because -ni already shows whose it is:
- Tunnen oloni itsevarmaksi. – I feel confident.
- Minun oloni tuntuu hyvältä. – My condition feels good. (more literally)

In everyday speech, you’ll often just hear the possessive suffix without the pronoun: oloni, taloni, ystäväni, etc.

Why is itsevarmaksi in the -ksi form as well? Could it be itsevarmalta or itsevarmana instead?

Itsevarmaksi is also in the translative case (from itsevarma = self-confident, confident).

itsevarma → itsevarmaksi

With verbs like tuntea (“to feel”), muuttua (“to change”), tulla (“to become”), Finnish often uses the translative to describe the resulting state:

Tunnen oloni itsevarmaksi. – I feel (my state) to be confident.
Hän tuli vihaiseksi. – He/She became angry.
Se tuntuu oudoksi. – It feels strange (as a state).

Using other cases changes the pattern and sometimes the meaning:

itsevarmalta (ablative) is more natural with tuntua:
- Minusta tuntuu itsevarmalta. – It feels confident to me / I feel confident.
itsevarmana (essive) can mean “in a state/role of being confident,” but in this specific construction with tunnen oloni, itsevarmaksi is the normal choice.

So in this exact sentence, itsevarmaksi (translative) is the standard, idiomatic form.

Could I change the word order to “Tunnen oloni itsevarmaksi, kun saan vaikean tehtävän valmiiksi”?

Yes, that is perfectly correct and natural.

Finnish word order is fairly flexible, especially between a subordinate kun‑clause and the main clause. Both:

Kun saan vaikean tehtävän valmiiksi, tunnen oloni itsevarmaksi.
Tunnen oloni itsevarmaksi, kun saan vaikean tehtävän valmiiksi.

mean the same thing. The choice mainly affects emphasis:

Starting with the kun clause puts more focus on the condition/time (“whenever this happens…”).
Starting with Tunnen oloni itsevarmaksi foregrounds the feeling, and then explains when it happens.

Why is the verb saan in the present tense, even though this can refer to future or general situations?

Finnish uses the present tense much more broadly than English:

Habitual/general statements
- Kun saan vaikean tehtävän valmiiksi, tunnen oloni itsevarmaksi.
  = Whenever I finish a difficult task, I (typically) feel confident.
Near future
- Huomenna saan tehtävän valmiiksi.
  = Tomorrow I will finish the task.

Finnish normally does not have a separate future tense; the present covers:

present time
near future
general truths/habits

Context and time expressions (like huomenna, ensi viikolla) clarify the exact time.

Can I just say “Tunnen itsevarmaksi” without “oloni” or “itseni”?

No, “Tunnen itsevarmaksi” is not grammatical by itself.

The verb tuntea (“to feel, to sense”) normally needs an object in this kind of structure:

tunnen oloni itsevarmaksi – I feel my condition/state to be confident
tunnen itseni itsevarmaksi – I feel myself to be confident

If you want to say “I feel confident” without an explicit object, a very common and natural alternative is:

Minusta tuntuu itsevarmalta.

So use one of these patterns:

Tunnen oloni itsevarmaksi.
Tunnen itseni itsevarmaksi.
Minusta tuntuu itsevarmalta.