The number of flats you have will increase geometrically as your patch supply shrinks.
The wind will always be at the back of the person riding in the opposite direction you are going.
The number of young children learning to ride their tricycles/wheels with training wheels will grow at the same rate as you feel in a rush.
Invariably, the next store selling pie will run out just as you arrive.
and
Extra water bottles left at home are an excellent forecaster of a parched, blisteringly hot ride.