The state of the world can change between steps and the next set of instructions don't apply til you meet some certain criteria or .. event, if you will.
> drive in your car on this street, turn left on Prune street, turn right on Elm street, the store will be after the second light.
Turn left on Prune street doesn't mean nothing else happened between you driving your car and reaching that street.
You could have stopped on the way to pick groceries, changed a tire, bought a snack ... you get the idea.
It doesn't mean you must drive straight to Prune or could get to the destination if you only drove straight there.
Getting to Prune street is an async call. When you reach it, regardless of how, a callback is fired and a new async task is given to you.
This is basically exactly how it happens. I say "Can you buy me a thing". The rest is automatically performed by your brain's programming. There is no need to actually mouth the instruction "if you are at home without the gadget, go to your car" because "Can you buy me a thing" automatically links against the code which includes that state processing function.
I could never understand how this works better as a mental model. Say you ask somebody to buy you a gadget in a store they don't know. What do you do tell them:
a) "drive in your car on this street, turn left on Prune street, turn right on Elm street, the store will be after the second light. Go there, find "Gadgets" isle, on the second shelf in the middle there would be a green gadget saying "Magnificent Gadget", buy it and bring it home"
or:
b) when you find yourself at home, go to car. When you find yourself in the car, if you have a gadget, drive home, otherwise if you're on Elm street, drive in direction of Prune Street. If you're in the crossing of Elm street and Prune street, turn to Prune street if you have a gadget but to Elm street if you don't. When you are on Prune street, count the lights. When the light count reaches two, if you're on Prune street, then stop and exit the vehicle. If you're outside the vehicle and on Prune street and have no gadget, locate store and enter it, otherwise enter the vehicle. If you're in the store and have no gadget then start counting shelves, otherwise proceed to checkout. Etc. etc. - I can't even finish it!
I don't see how "steps to follow" is not the most natural mental model for humans to achieve things - we're using it every day! We sometimes do go event-driven - like, if you're driving and somebody calls, you may perform event-driven routine "answer the phone and talk to your wife" or "ignore the call and remember to call back when you arrive", etc. But again, most of these routines will be series of steps, only triggered by an event.