When I first played Outrun, I didn't know that space bar was to go into high gear. I played Outrun dozens of times at about only 195 KM/H and kept failing to get to Stage 2. But when I discovered that space bar high gear, wow!
Tell us about your one-key breakthroughs (or something else simple that made you go from loser to winner very fast).
Learning about extended jump in Half-Life (not the long jump module)... until then I kept on jumping in radioactive goo and missing most of the power-ups on high crates.