Tony Fadell, the one of the originators of the iPod, explains it in his TED talk, "The first secret of design is…noticing." Noticing little things is hard because the brain habituates operations it does often. He uses the example of driving. First time you drive you notice every button, switch, pedal and everything outside the car. Once you are an experienced driver, the driving process has been habituated by your brain. You notice only the things you need to drive the car. You can now talk and listen to music and still perform the driving.
Unfortunately, that same habituation works against seeing little things that can make a difference. Fadell mentions when designing the iPod, Steve Jobs continually told the designers to...stay beginners, see things as they do. Learning designers do good to think the same way. Not "dumbing" down content, but rather, looking at ways to integrate the message or process in a simple fashion. A familiar subject could take on new meaning. Something that was there all the time, but habituation blinded the designer.
Fadell went on to invent the Nest thermostat on the same principles. He noticed the first thermostats were simple, a user set a temperature and walked away. But later designers added so many options, timers and programming - a user needed a manual just to turn it on. (Nest puts all of the options into the invisible programming to keep the UI as simple as the original thermostats.) Sound familiar?
Have you noticed the same engineering in products, software and learning processes you have to use? They are so heavy with options, it's impossible to simply turn it on and use it. I've seen training designs-- that required training to use. Is that an oxymoron?
At any rate, I highly recommend watching the talk to refresh your "noticing" muscles.