Good old dear me sitting comfortably and writing some code...
Suddenly, the doorbell rings!!!
"One moment! Coming!", I shout...
I proceed going to the hall, take the keys from the table right next to me and I unlock the door...
I open it and there's only thin air in front me. Downstairs I hear the building door closing and the elevator working its way up, higher than my floor...
I close the door and I go back to my desk, resuming my work and thinking:
"I don't know who are, I don't care who you are, but I will find you and I will make you pay..."

Now my coding train of thought has stopped! Thanks, unknown doorbell ringer!!!