This image (and ones like it) is so valuable:
http://adit.io/imgs/functors/fmap_def.pngEvery time you read about things even tangentially related to functional programming, you inevitably arrive at a slop of letters with arrows between them. Even just parsing that is rather difficult for non-initiates, let alone trying to grasp what it's actually saying after you've parsed it. Words and arrows (the normal kind of arrows, the kind that are for pointing at things) can help a lot.
