Kierkegaard

And no Grand Inquisitor has in readiness such terrible tortures as has anxiety, and no spy knows how to attack more artfully the man he suspects, choosing the instant when he is weakest, nor knows how to lay traps where he will be caught and ensnared, as anxiety knows how, and no sharpwitted judge knows how to interrogate, to examine the accused as anxiety does, which never lets him escape, neither by diversion nor by noise, neither at work nor at play, neither by day nor by night. 

                                 SØREN KIERKEGAARD