First diagram on https://programmingblockchain.gitbook.io/programmingblockchain/introduction/diagrams is anything but clear. English generally reads left to right and top to bottom and arrows indicate movement in a particular direction. Without the explanation above it, the sample diagram looks like it means

key {somehow relates to (fits in?)} padlock
password {somehow relates to} the same padlock
results in key
password {somehow relates to} key

It would be clearer as

but then someone would have to update all the other diagrams.