why is myslet associated with si all of a sudden?
The particle "si" is the dative form of "se". You can think of "myslím si" as meaning "I think to myself". But "myslet si" is more common in Czech than "think to oneself" is in English.
Could SI be omitted in this sentence (or replaced by SE)?
I'm also curious how the 'si' works here
Why "sometimes" is not valid here?
Why should it be valid? "Sometimes = někdy, often = často"
I typed, "I do not often know what to think," as answer, but it was counted as incorrect. Wouldn't this be acceptable also?
As an English speaker, that sounds more natural. "Often I do not know .." sounds okay to
"Often I do not know what to think" is an accepted translation.
This alternative has been added.