This is from Rainer Maria Rilke’s Letters to a Young Poet—one of the most beautiful pieces of writing advice ever put to paper:
You ask whether your verses are good. You ask me. You have asked others before. You send them to magazines. You compare them with other poems, and you are disturbed when certain editors reject your efforts. Now (since you have allowed me to advise you) I beg you to give up all that.
You are looking outward, and that above all you should not do now. Nobody can counsel and help you, nobody. There is only one single way. Go into yourself. Search for the reason that bids you write; find out whether it is spreading out its roots in the deepest places of your heart, acknowledge to yourself whether you would have to die if it were denied you to write.
This above all — ask yourself in the stillest hour of your night: must I write? Delve into yourself for a deep answer. And if this should be affirmative, if you may meet this earnest question with a strong and simple “I must,” then build your life according to this necessity; your life even into its most indifferent and slightest hour must be a sign of this urge and a testimony to it.
Then draw near to Nature. Then try, like some first human being, to say what you see and experience and love and lose.
Therefore, my dear sir, I know no advice for you save this: to go into yourself and test the depths in which your life takes rise; at its source you will find the answer to the question whether you must create. Accept it just as it sounds, without inquiring into it. Perhaps it will turn out that you are called to be an artist. Then take that destiny upon yourself and bear it—its burden and its greatness—without ever asking what recompense might come from outside. For the creator must be a world for himself and find everything in himself and in Nature to whom he has attached himself.
But perhaps after this descent into yourself and into your inner solitude you will have to give up becoming a poet; (it is enough, as I have said, to feel that one could live without writing: then one must not attempt it at all). But even then this inward searching which I ask of you will not have been in vain. Your life will in any case find its own ways thence, and that they may be good, rich, and wide I wish you more than I can say.
What more shall I say to you? Everything seems to me to have its just emphasis; and after all I do only want to advise you to keep growing quietly and seriously throughout your whole development; you cannot disturb it more rudely than by looking outward and expecting from outside replies to questions that only your inmost feeling in your most hushed hour can perhaps answer.
Know Thyself 