…For example, if a Goal says that three out of five Keepers shown are needed to win that Goal, and I have four of those Keepers, must I discard all four, or can I choose which three to discard, and which one I will keep in play?

A: You don’t have to discard all the Keepers mentioned, only enough to gain the Goal, so you get to pick which Keepers you will discard, and which will stay in play.