Ross explained it well enough, but I would like to expand if I may.
In Monsters and Other Childish Things, you play as a kid who has a pet monster. My monster was an alligator in a trenchcoat who cried cream cheese tears named "Mr. Mojo Risen." When he wasn't a monster, he turned himself into a lunchbox that I carried with me everywhere I went.
That particualr session featured a boy that was killed at his home and the spirit of the boy was hauting our school. The ghost of the boy was down in the boiler room of our school and I was able to phase through the door (because Mojo could phase through things) and I was able to talk to the boy. Meanwhile, the other players were investigating the boy's house and the ghost was there too.
Essentially, Ross had forgotten I could phase through things and like any good GM, he made up something on the fly to keep the plot going and give my character a reward for quick thinking.
At the end of the game, some of the players were a little confused. "Why was the boy in the boiler room?" they asked. "Well . . . his spirit was restless and . . . " Ross tried to justify, but Tom was relentless.
Tom said something along the lines of, "That doesn't makes any sense" and I replied, "There are Monsters in the school Tom!"
Essentially, the line is for anything that requires a suspension of disbelief. I mean, let's face it, we're all role-playing characters that can do incredible feats of athletics and bravery, not to mention magic, but we can't suspend our disbelief that a ghost can be in two places at once? It's just ridiculous.
