Relative pronoun after superlatives (mikä)

Normally, Finnish uses the relative pronoun joka to refer back to a specific noun. However, mikä replaces joka in two key situations.

1. After Superlatives

If the noun being referred to is modified by a superlative adjective (e.g., "the biggest," "the best"), use mikä. It takes case endings to match its grammatical role in the relative clause, such as the object form minkä.

That was the greatest insight that I have ever received.
Se oli suurin oivallus, minkä olen koskaan saanut.
This is probably the most unpredictable ordeal that we will experience.
Tämä lienee arvaamattomin koettelemus, minkä koemme.
That is probably the most meaningful decision that I made.
Tuo lienee merkityksellisin päätös, minkä tein.
Maturity is the best thing that an ordeal can teach.
Kypsyys on paras asia, minkä koettelemus voi opettaa.

2. Referring to an Entire Clause

Use mikä when "which" refers to the entire preceding thought or situation rather than a single noun.

A big mistake came to be made, which I realized later.
Tuli tehtyä suuri virhe, minkä oivalsin myöhemmin.

If the pronoun is the subject of the relative clause, it remains in the nominative form mikä.

The change of direction required daring, which was not easy.
Suunnanmuutos vaati uskallusta, mikä ei ollut helppoa.
Life is unpredictable, which requires self-confidence from us.
Elämä on arvaamatonta, mikä vaatii meiltä itseluottamusta.