To err is human, but to really foul things up you need a computer.
No action is without side effects.
There's no such thing as a free lunch.
People will accept your idea much more readily if you tell them Benjamin Franklin said it first.
Each problem solved introduces a new unsolved problem.
The only way to discover the limits of the possible is to go beyond them to the impossible.
Batteries are not included.
If you explain so clearly that nobody can misunderstand, somebody will.
If anything can't possibly go wrong, it will anyway.
Anything that can go wrong, will.