Player #1 contends that he won the game because the rules say that as soon as a goal is achieved the game is over and no other actions/cards can be played. Player #2 says that no, the Surprise card overrides the general rule and cancels the playing of the goal and therefore the game does not end. Which is true?

A: Yes. If the Canceled Plans card played is played immediately, it cancels the Goal and play continues to the next person. That is the intent of the card.

It works the same way for That’s Mine. If the winning play is a Keeper, That’s Mine can be used to cancel that play, preventing the win.

Again, Surprises are meant to be able to work this way… but you have to be using the correct Surprise for the type of play you’re canceling – and you must play your Surprise in a timely manner: say, within a few seconds of the player playing their card.

For more nuanced suggestions about how to resolve some tweaky timing issues, check
When a player is allowed multiple plays on their turn, are there any guidelines for timing between plays?”