Many game systems have a surprise mechanic, which gives one side in a combat encounter the advantage of doing something before the other side can react or prepare. This of course echoes reality, where combatants with the element of surprise have a big advantage in the initial stages of a fight.

So getting the surprise advantage is an important bit of tactical roleplaying, that players are often prepared to put considerable effort into achieving.

Which makes it all the more fun when it goes horribly wrong and they end up on the wrong end of the surprise stick.

Transcript

GM: Roll for Stealth.
Chewbacca: 18.
Han: 1.
[SFX]: stick!
GM: The closest trooper looks directly at you.
Chewbacca: I daresay our element of surprise hath snapped in twain.
C-3PO: I think they've twigged onto you.
Luke: Now you've stepped in it.
GM: Sorry to break in, but: they get a surprise action.
[SFX]: Smack! {trooper near Han hits him}
GM: The other one flees into the forest on his bike. Chewbacca?
Chewbacca: <sigh> I fire my plasma crossbow.
[SFX]: Pow!
Han: Hey, can I try that?
Chewbacca: Never.