And your doubt can become a good quality if you train it. It must become knowing, it must become criticism. Ask it, whenever it wants to spoil something for you, why something is ugly, demand proofs from it, test it, and you will find it perhaps bewildered and embarrased, perhaps also protesting. But don't give in, insist on arguments, and act in this way, attentive and persistent, every single time, and the day will come when, instead of being a destroyer, it will become one of your best workers--perhaps the most intelligent of all the ones that are building your life.

Rainer Maria Rilke, Letters to a Young Poet,