Murphy's law

At table this afternoon we were talking about the various possibilities of things going 'wrong' with children and computers.  Someone spoke of 'Murphy's law.  I thought he was talking about some physicist but no.  The law he said is this

Anything that can go wrong, will go wrong!

So the whole idea was to have the system being created or constructed having taken into consideration all that can go wrong and thereby eliminating those possibilities.

More about the law itself, here.

Another example:
The printer will jam the moment you leave the room assured that all is right!