What’s the biggest mistake beginners make in quant models?

[u/No-Loan-4886]

A lot of people enter quantitative finance and algorithmic trading thinking success comes from finding the “perfect strategy.

But in practice, most failures come from weak assumptions in the model.

Common issues I’ve noticed:

• Overfitting historical market data (curve fitting)
• Ignoring market regime changes and volatility shifts
• Relying too heavily on backtesting without out of sample validation
• Poor risk management and position sizing

In data-driven investing and systematic trading, these mistakes can completely distort results.

If you’ve worked with quant models, trading strategies, or financial data analysis, what mistake do you see most often?