In my case, the first time I can taste a consistent profit because I did the backtest. Yes, you will never 100% believe that the backtest result will be same as forward test, or actual trading.
I don't know how to program so I used spreadsheet to backtest my system. As far as I concern, the things make the result in reality differ from the backtest result because of,
- Human error (inconsistant following trading plan)
- Market uncertainty (well, that's the case...)
Through practice I think we can overcome human error. As for market uncertainty, well, we do need to calibrate a little bit of our system in certain period. Our trading system need to be robust and flexible. I do monthly analysis to identify weakness in my system. If I detect one, then some setting need to change. So far its ok.
I strongly feel trade without backtest is like driving car with eyes close. At least it give us more confidence in our trade. Of course, after backtest, we need to do the forward test for optimization. After this then the system will complete. I dont think any system will forever work unless we do the calibration in certain period or something like that.
Have a nice pips!