I thought it was this:
Order Sandwich --> Pay for sandwich --> Receive Sandwich --> Eat Sandwich.
Am I missing something here? Is it really more complicated?
Well yes you see you have 4 different cases there. That's just one possibility. You are missing the other 23 permutations. In all you have:
Order Sandwich --> Pay for sandwich --> Receive Sandwich --> Eat Sandwich
Order Sandwich --> Pay for sandwich --> Eat Sandwich --> Receive Sandwich
Order Sandwich --> Receive Sandwich --> Pay for sandwich --> Eat Sandwich
Order Sandwich --> Receive Sandwich --> Eat Sandwich --> Pay for sandwich
Order Sandwich --> Eat Sandwich --> Pay for sandwich --> Receive Sandwich
Order Sandwich --> Eat Sandwich --> Receive Sandwich --> Pay for sandwich
Pay for sandwich --> Order Sandwich --> Eat Sandwich --> Receive Sandwich
Pay for sandwich --> Order Sandwich --> Receive Sandwich --> Eat Sandwich
Pay for sandwich --> Receive Sandwich --> Eat Sandwich --> Order Sandwich
Pay for sandwich --> Receive Sandwich --> Order Sandwich --> Eat Sandwich
Pay for sandwich --> Eat Sandwich --> Receive Sandwich --> Order Sandwich
Pay for sandwich --> Eat Sandwich --> Order Sandwich --> Receive Sandwich
Receive Sandwich --> Order Sandwich --> Pay for sandwich --> Eat Sandwich
Receive Sandwich --> Order Sandwich --> Eat Sandwich --> Pay for sandwich
Receive Sandwich --> Pay for sandwich --> Order Sandwich --> Eat Sandwich
Receive Sandwich --> Pay for sandwich --> Eat Sandwich --> Order Sandwich
Receive Sandwich --> Eat Sandwich --> Order Sandwich --> Pay for sandwich
Receive Sandwich --> Eat Sandwich --> Pay for sandwich --> Order Sandwich
Eat Sandwich --> Order Sandwich --> Receive Sandwich --> Pay for sandwich
Eat Sandwich --> Order Sandwich --> Pay for sandwich --> Receive Sandwich
Eat Sandwich --> Pay for sandwich --> Receive Sandwich --> Order Sandwich
Eat Sandwich --> Pay for sandwich --> Order Sandwich --> Receive Sandwich
Eat Sandwich --> Receive Sandwich --> Pay for sandwich --> Order Sandwich
Eat Sandwich --> Receive Sandwich --> Order Sandwich --> Pay for sandwich
So you see it's MUCH more complicated than you first thought!