closer than you think

Many parallels can be made between driving a manual transmission car and running a steam locomotive. The johnson bar works very similar to the gear shift. At light to moderate loads hooking up the johnson bar does the same thing as shifting to a higher gear (you go faster with the same throttle position). If you drop the bar down, you slow down (just like downshifting). With heavy loads, dropping the johnson bar gives you more speed and power, just like shifting your car to a lower gear climbing a hill or towing a trailer. One of the tricks to learn is where the crossover point of "moderate work to heavy work" happens. It's at a different point on each engine and it varies with grade, speed and load.
It's one of them "Zen" things......
It's not rocket science, but having a good ear to hear what the exhaust is telling you, a good feel about whether your speeding up, slowing or holding your own, knowing where you are and what's ahead on the road, where the slack is in the train, etc. keeps your mind in motion.
Now, if you're good, you can set things just right and ride for miles and not touch a thing. Then you have time to enjoy the ride and wave at the pretty girls.........