Investors in commodities often make common mistakes that can harm their returns. These include neglecting thorough research, attempting to time the market, overlooking diversification, ignoring risk management, neglecting storage and transport costs, making emotionally driven decisions, underestimating leverage and margin risks, neglecting macro factors, lacking patience, and not seeking professional advice. By avoiding these mistakes and adopting a disciplined and informed approach, investors can improve their chances of success in commodity investing.