When an investigator lands on a face down Arkham adventure card does he have to do the text on the back of the card or is it optional? Reading the rules it looks like in one section that the investigator "may" and in other that the investigator "resolves" the text.

You "may" resolve the effects whose wording is "you may" (for example: "you may spend 2 trophies to gain X effect"), you "must" resolve all the others, when the specific conditions are triggered (for instance: "At Midnight: a gate appears": this is an absolute clause)

Hope this helps

JULIA