According to the FAQ 2.2, Pawn Should read: “Whenever you make a successful run while Pawn is hosted on a piece of ice, move Pawn to the piece of ice directly after the current ice hosting Pawn, if able..."
I'm responding to a 7-year-old comment here, but what the heck. The issue with the card as written, if I understand it, was that when you installed Pawn, it was unhosted. Because the "successful run" trigger as written didn't require Pawn to be hosted on a piece of ice, the ability would still trigger if Pawn was unhosted. You wouldn't be able to move Pawn to the next innermost ice, so the "if you cannot" part of the trigger would fire. You'd get the Cäissa fetch as if you'd marched Pawn all the way through your opponent's ice, but without doing the hard work. I assume the idea was your Pawn could be "promoted" to another Cäissa after reaching your opponent's side of the board (evoking pawns in chess), but the ability as written allowed you to bypass that entirely by never hosting Pawn.— StaticSky