UserInterface                   BusinessLogic
     |        
 user input   
     |                               
     |------------------------------>|
                                     |
                               do some action
                                     |
     |<----------failure-------------|
     |                               
  handle the error
     |                               
     |


##</code><code>##


UserInterface                   BusinessLogic                 UserInterface
     |
 user input
     |
     |------------------------------>|
                                     |
                               do some action
                                     |
                                     |----------failure------------->|
                                                                     |
                                                             handle the error
                                                                     |
                                                                     |