Example: Chris is playing a deck with Brobnar, Mars, and Sanctum. Chris plays Hypnobeam to take control of a Saurian creature from Sam. On Sam's turn, Sam plays Mark of Dis and targets the Saurian creature, but doesn't destroy it, forcing Chris to choose Saurian for their active house next turn. Sam then subsequently plays a card that destroys the Saurian creature in Chris' battleline. On Chris' turn, when they reach the Choose a House step, they are forced to choose a house that they cannot choose as it is not on their identity card and they don't control a card of that house. Since Cannot effects take precedence, Chris may freely choose their active house.