There are plenty of conventional knowledges that are perceived to be true but in reality are very trivial (situationally correct). We had a lot of these with discretionary trading like.... 1. Trend related.: - Trend is your friend. - Cut your losses short, let your profits run. Reasons for it being trivial: Mean Reversion + Martingale, Stat. Arb. Scalping. Intraday Swing Trading. Historical conditions of the market those days, unlike the markets now. 2. Technical Analysis: - Market is always right. Reasons for it being trivial: The usage is completely dependent on the trader using it, ending up as a self-fulling prophecy. And there's plenty of statistical confirmations that general usage does not provide any significance (actually negative). 3. Psychology thing... it's trivial. etc. etc. There's plenty of them in Systematic Trading... 1. Testing with large data. 2. Out-sample/Forward Testing. 3. Robustness / Non curve-fit models. 4. Using stops. 5. Sharpe Ratio. 6. Pretty much most of the trading rules/lexicons brought over from discretionary trading. 7. Flipping coins analogy. I tend to see way too many people caught up with outdated and factless information.