If the price moves against you (down if you have written a put, up if you have written a call) then you never get the chance to buy the options back at a profit

If the price moves against you (down if you have written a put, up if you have written a call) then you never get the chance to buy the options back at a profit. You might get a bit of theta decay, but equally any large moves will tend to kill you on the gamma and vega. As I said in another comment, writing options covered or not is basically a bet against volatility.