Every metric is designed to break down, unless it’s a complex metric. Active share, a metric pioneered by Martijn Cremers and Antti Petajisto, is widely regarded as a hallmark of evaluating active management. The metric quantifies the proportion of a portfolio's holdings that differs from its benchmark index. It serves as a key indicator of how actively managed a portfolio is, with higher active share values indicating greater deviation from the benchmark. If you have high active share you are an active manager, if you are low active share, your process is passive. And if your process is passive, you are merely replicating the benchmark, you are not designed to deliver alpha.