Learn Finnish: Jos haluaa ehkäistä stressiä, täytyy levätä tarpeeksi. - If one wants to prevent stress, one must rest enough.

This is the generic zero-person construction, which is the focus of this lesson. By using the third-person singular verb haluaa without a subject, it translates to 'one', 'anyone', or 'you' in a general sense.

Normally täytyy requires a subject in the genitive case, like 'minun'. Why isn't there one here?

To make a necessive verb like täytyy generic (meaning 'one must'), you simply leave out the genitive subject. Because the first clause establishes the general 'one' with haluaa, the second clause naturally continues it by leaving täytyy subjectless.

Why is stressiä in the partitive case here?

Abstract, uncountable concepts like stressi usually take the partitive case when they act as an object. Additionally, the verb ehkäistä (to prevent) expresses an action without a defined endpoint, which also triggers a partitive object.

The word tarpeeksi means 'enough', but it has the translative case ending -ksi. Why?

The word tarpeeksi is formed from the noun tarve (a need) plus the translative ending -ksi. In Finnish, the translative case is frequently used to turn nouns or adjectives into adverbs. Literally, it means 'for a need', which gives us the everyday meaning 'enough'.