Hey, I *was* an orchestral triangle player- at least in high school- and let me tell you, there are more "exposed" parts for triangle than just about any instrument. Face it, when you leave out a note playing DB in a section, no one hears it. Even if you play the wrong note, only the people around you hear it. But just try coming in a little off the beat on a triangle part...!
I was the utility infielder in my HS orchestra, handling xylophone, orchestra bells, tubular bells, bongos, gong, everything that involved counting 80 measures, coming in for a couple, and disappearing for another 80. And let me tell you, there's no better way to piss off your conductor than to miss that triangle cue. ;-)