Learn Finnish: Minä en pidä shakista, koska se on vaikea peli. - I do not like chess, because it is a difficult game.

This is because of the verb pitää (to like). In Finnish, certain verbs demand that the words connected to them take a specific case ending. This is called a verb rection. When you use pitää to mean to like, the thing you like must be in the elative case, which means adding -sta or -stä.

The dictionary word for chess is shakki with a double k. Why does shakista only have one k?

This is due to consonant gradation, a rule where consonants change when grammatical endings are added. Adding the -sta ending closes the last syllable of the word. When this happens, the strong double kk weakens into a single k.

If this lesson is also about the verb tykätä, could I use that instead of pitää?

Absolutely! Both pitää and tykätä mean to like, and both require the exact same elative ending. If you used tykätä, the sentence would start with Minä en tykkää shakista. Tykätä is a little bit more common in casual, spoken Finnish.

Why is the verb form pidä and not the dictionary form pitää after the negative word en?