私はあのとき父がいったことを決して忘れないでしょう。

I; me; private affairs; personal matter; secrecy; selfishness

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

that (someone or something distant from both speaker and listener, or situation unfamiliar to both speaker and listener)

regular (stops at every station) Jouetsu-line Shinkansen

father

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to do up (hair); to braid; to fasten; to fix

thing; matter; incident; occurrence; event; something serious; trouble; crisis; circumstances; situation; state of affairs; work; business; affair; after an inflectable word, creates a noun phrase indicating something the speaker does not feel close to; nominalizing suffix; pretending to ...; playing make-believe ...; alias; aka; nickname; alternative name; also known as

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

never; by no means; not in the least; in no way

to forget; to leave carelessly; to be forgetful of; to forget about; to forget (an article)

death