Run the numbers yourself. The financial industry struggles with data integrity, and I’ve found plenty of errors in stock screeners, financial-data services, and spreadsheet templates. Some issues require careful judgment, such as excluding non-recurring or special items from earnings. Accounting isn’t always black and white, despite best intentions.

By personally verifying the data and calculations, you can avoid making investment decisions based on faulty information. This approach is a lot of work, but can significantly improve your performance over time. Always check primary sources like SEC filings and cross-reference data from multiple reliable sources.

As you develop your skills, learn to read financial statements thoroughly and create your own analysis tools. Remember that the results from your decisions depend on the accuracy of your data and the quality of your analysis.