Backtesting is necessary to develop a system but not sufficient to prove YOU can make money. In this video Seth Freudberg discusses:

• Mid-prices not easy in fast market
• Testing software data may be imperfect
• Mid-price may be a distortion—synthetic equivalent may be more accurate.
• Multiple trades means you may not be attending to the one being tested.
• Emotion—do you have the strength to follow your plan—the riskier, the less likely.

Enjoy the video.

* no relevant positions