A lesson in folly is worth two in wisdom. - Tom Stoppard

Bakunin: Act first! The ideas will follow, and if not — well, it's progress

Now a philosopher exploring the difficult terrain of right and wrong should not be over-impressed by the argument "a child would know the difference". But when, let us say, we are being persuaded that it is ethical to put someone in prison for reading or writing the wrong books, it is well to be reminded that you can persuade a man to believe almost anything provided he is clever enough, but it is much more difficult to persuade someone less clever.

We're better at predicting events at the edge of the galaxy or inside the nucleus of an atom than whether it'll rain on auntie's garden party three Sundays from now.