Though not specific to automated trading systems, traders who employ backtesting techniques can create systems that look great on paper and perform terribly in a live market. Over-optimization refers to excessive curve-fitting that produces a trading plan unreliable in live trading. It is possible, for example, to tweak a strategy to achieve exceptional results on the historical data on which it was tested. Traders sometimes incorrectly assume a trading plan should have close to 100% profitable trades or should never experience a drawdown to be a viable plan. As such, parameters can be adjusted to create a “near perfect” plan — that completely fails as soon as it is applied to a live market.