I think all the skills mentioned matter, but if I had to choose one it'd be the ability to adapt to the current table situation, because the game itself is always the "same": NLH deepstack. There is no ICM pressure, there is no variation in effective stacks. Every table is different, and the players who keep using the same strategy against everyone leave money on the table. Adjusting to nits, maniacs, calling stations, or aggressive regs is what turns a decent player into a consistent winner.
Of course, if you play Zoom/Rush/anything that is not a fixed table, this is a bit more difficult, but you'll be able to collect data from opponents here and there, and might face them again in the future.