State Machines — Simple

stateDiagram-v2
  [*] --> Created
  Created --> Paid : pay()
  Created --> Cancelled : cancel()
  Paid --> Shipped : ship()
  Paid --> Refunded : refund()
  Shipped --> Delivered : deliver()
  Shipped --> Returned : return()
  Delivered --> [*]
  Refunded --> [*]
  Cancelled --> [*]
  Returned --> [*]

A finite state machine = (states, transitions, events, guards). Anything with a lifecycle — order, booking, ATM card, elevator cabin, video player — is a state machine. Model it explicitly; don't bury transitions in if-chains.