This could be mechanical things like the order of adjectives, or more complex/personal things on your journey of learning another language.
I want to start learning Norwegian again and I remembered learning a lot about citrus fruits as I went on Wikipedia adjacent trips.
I like that the Spanish grammar is really close to the real uses or the language. The same with English…In Portuguese we have a language we learn from the grammar and almost another we actually use in out daily lives. In Brazil we learn a lot of verb conjugations that we don’t use without sounding too formal or pedantic. We also learn conjugations with pronouns like “tu” and “vós” that are not used in Brazil.