KPI (Key Performance Indicator)

Before building a new feature, say a recommendation system on an e-commerce platform, defining the KPI (average cart value increase, click-through rate) sets a clear way to judge success from day one. Three months after launch, the team can look at that specific number instead of relying on a general impression or anecdotal user feedback.

A common mistake is tracking vanity metrics, like visitor counts or downloads, that don't tie to any concrete decision. A good KPI should answer the question "if this number drops, what do we change?" It's better to track two or three genuinely actionable KPIs than a dashboard with twenty metrics nobody actually looks at.