What is reinforced, is repeated.

It’s not what you don’t know that hurts you.  It’s what you think you know that ain’t so.

Once is accident; twice is coincidence; three times is enemy action.

There is no way that a writer of fiction can compete with real life for its pure absurdity. — Ed Driscoll

In explaining any puzzling Washington phenomenon, always choose stupidity over conspiracy, incompetence over cunning. Anything else gives them too much credit. — Charles Krauthammer

Everything you do has unexpected consequences.

So does not doing anything.

The human mind is so good at seeing patterns that if there are no patterns, it will make them up.

If enough things happen, then even very very improbable things will eventually happen.

If something can’t go on forever, then it won’t. — Megan McArdle

Actually picked this up from Glenn Reynolds, Megan is the earliest version I can find easily. As always, corrections are gratefully accepted as long as they’re right.

Update: Aha! It’s Stein’s Law:

If something cannot go on forever, it will stop.

Thanks to reader sourcreamus in the comments.

“No battle plan survives contact with the enemy”