A phenomenon which often occurs in games is that a player will start coming up with explanations or revelations about the plot that the GM had absolutely no hand in. At this stage, it's fine, since that's a simulation of the what the characters are doing - trying to understand what's going on around them.

Things get interesting when what one player says becomes so compelling that the other players start taking it as the truth, believing it in preference to what the GM actually has planned or says in contradiction.

Transcript

Obi-Wan: We need to avoid the droid army and find this queen. But she's on the other side of the planet.
Qui-Gon: We start walking.
Obi-Wan: ... away from the droids.
GM: Right. You come across a shoreline. You're clearly going to need to find some form of transport.
Qui-Gon: Jar Jar, any ideas?
Jar Jar: Mesa takes you to mesa city!
GM: City? What? Wait a second...
Jar Jar: It'sa underwater!
GM: Underwater??
Qui-Gon and Obi-Wan: Cool!