Observation
It's easier to put a cover on a futon than a duvet (quilt).
Loose paper breeds rapidly.
Objects can move from box to box by quantum tunnelling, disappearing from the box you left them in, and appearing in the box you just searched.
If one person brings bagels to work, the probability of someone else doing it on the same day is 80% or higher.
Sofas grow to avoid being moved to another room.
Cats have bones made of rubber.
Tidiness of a house is inversely proportional to length of time before visitors arrive.
Never attempt to assemble furniture on an empty stomach.