A slice of buttered bread will, when dropped, will always land butter-side down
Buses take ages to arrive, but when they do they always arrive in sets of three (in Britain "you wait ages for a bus, then two come along at once!").
When graphing, the graph paper is always one square too small for the perfect scale
When caught in a traffic jam, the lane that you are in will always be the slowest to move
Nothing is as easy as it looks.
Everything takes longer than you think. Or, everything takes twice as long as it should; excepting that which appears easy, taking three times as long.
Anything that can go wrong will go wrong, and at the worst possible time.
If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong.
If something simply cannot go wrong, it will anyway.
If you perceive that there are four possible ways in which a procedure can go wrong, and circumvent these, then a fifth way, unprepared for, will promptly develop.
Left to themselves, things tend to go from bad to worse.
If everything seems to be going well, you have obviously overlooked something.
Nature always sides with the hidden flaw.
It is impossible to make anything foolproof because fools are so ingenious.
Whenever you set out to do something, something else must be done first.
Every solution breeds new problems.
Change is inevitable, except from a vending machine.
A Smith and Wesson beats four aces.
Junk will grow to fill the available cupboard space.
All small objects of value will disappear when set down.
Magellan's Allegory: If you stop and ask someone for directions, and they tell you "You can't miss it"...then be assured that you will.
If you sellotape two cats together, back to back, and drop them off a building, inevitably they will land sideways.