AI adoption is rapidly increasing, but the success rates of AI projects are concerning, with failure rates rising from 17% to 42% in 2025 due to issues like the evaluation gap, where models perform well offline but fail under live conditions. The Area Under the Curve (AUC) metric, which measures a classifier's ability to separate classes across all thresholds, offers a more reliable signal than traditional metrics like accuracy, especially as data and business requirements change. However, many teams misuse AUC as a scoreboard, leading to inflated model scores and hidden failures. AUC is particularly valuable in industries like healthcare, finance, and content moderation, where it aids in balancing sensitivity and specificity without committing to a specific threshold early on. Calculating AUC accurately requires understanding the ROC curve and using techniques like the trapezoidal rule, while specialized metrics like PR-AUC are more suited for imbalanced datasets. Implementing AUC in production involves challenges such as infrastructure limitations, organizational politics, and modeling traps, which can lead to discrepancies between staging and production performances. To address these, monitoring tools like Galileo offer a comprehensive solution by providing automated evaluation metrics, real-time monitoring, and compliance features to prevent AI project failures.