Everybody gets told to write about what they know. The trouble with many of us is that at the earlier stages of life we think we know everything- or to put it more usefully, we are often unaware of the scope and structure of our ignorance.
Man is better without knowledge of things to come, for what is to be will be, and man can neither avert nor hasten. It is better to go in the dark when the road must pass a lion and there is no other road.