For the sentence “This course deals with the facts that
everyone should know”, the adjective clause is “that everyone should know”. In
the given sentence the main clause is “This course deals with facts”. The adjective
clause is actually describing the main clause. Adjective clause is a clause
that is mainly used to describe the main clause or a noun or a pronoun. So
adjective clauses are actually subordinate clauses having the sole purpose of
describing the main clause of the sentence.
I believe he means that in the Caribbean people died so young that he imagines it so often. He thinks he needs to make any happy/good moment last so he remembers that.
