The saying originated in the U.S. Military during World War 2 as a sarcastic comment about standard operating procedures. Snafu is now used to indicate any foul up. If you are ignoring the skirmish in front of you, convinced it is a feint, it will turn out to be the main assault. Your ability to locate a speed loader for your clips will depend on whether someone is shooting at you.
Tracers work both ways.
In the absence of cigarettes and chow there is always coffee. The best way to tell if a patrol will be dangerous is when the new Second Lieutenant tells you no activity is to be expected. When you want it done wrong, tell the new 2nd Lt to do it. The most dangerous thing in the military is a brand new 2nd Lt with a map, a flashlight and some vague notion of something to do. The best man between a private and a 2d Lt is the private.