Whether you're discretionary or mechanical, it all boils down to one thing: PRICE PATTERN. Find the profitable pattern and stick to it, come rain or shine. However, in order to find a pattern, you need the help of a backtest.
I would agree with this wholeheartedly. I just wouldn't necessarily make it an automated backtest. And I find my price patterns (usually) by experimenting with the data.
Price pattern need not be limited to chart patterns. It could be a pattern of price flow, eg. DOM. But you need a price pattern nonetheless to become a profitable trader. And I want to stress that it must be "consistently applied".