First, when I was a new conductor, I was a brakeman on a yard switch job. We were flat switching without air, and the foreman kicked a car and it stalled on the lead. I went to the car and had the engineer make the hitch, while the foreman was at the head of the next car. The couplers bypassed on the stalled car, and I said on the radio, "the hitch didn't make." The foreman thought that the pin didn't drop, so he called for a second kick instead of re-doing the hitch - the engineer poured on the power, the stalled car lurched sideways, and the rail turned over spilling the cars on the ground, right where I was standing. I ran like a sissy, but damn that was something I didn't need to see a few months into my career.
Second, I was a spare board engineer on a local, and we were running short on time. The moves we needed to make required splitting the power and a couple of other things, and we had a lot of cars. After I mated the engines back up after that, I was light engines and coming into a speed restriction, so I put on a little independent - NOTHING. I didn't have 10 seconds to wait for the dynamic, and had no cars, but I put on some automatic anyway and that worked. After slowing down, I looked down, and sure enough, I had forgotten to cut in the independent (the auto was fine though).
Come to think of it, the best one was when I was a spare engineer on a local job with a conductor that was in too much of a hurry. I was new and was trying to do everything safely, and he was in a hurry to make a commuter window. He egged me on to shove him faster toward a siding, and as I was speeding up, he suddenly told me to hold up, as a switch was wrong and I was headed straight for a cut of cars! I shot 'em, but we still made a hard hitch. First night on the job, and I damn near killed the guy. Since then, I read on a company bulletin that, "there is a difference between working with a sense of urgency, and working dangerously." I take that to heart these days - I am in NO hurry.