Cohort analysis is a staple of financial and product analytics you group data by time period and track how each cohort behaves across subsequent periods. The visualization is a matrix: cohorts on the rows, time offsets on the columns, values in the cells. Sounds simple. The implementation is anything but, especially when you add interactivity. I built this cohort analysis chart for financial trading analytics — a 13×14 interactive matrix with keyboard navigation, live timer cells, row/column highlighting on selection, and a detailed buy/sell order popup. Then, as an experiment, I asked AI to generate the same component from scratch. The results revealed something important about where AI-assisted development genuinely helps and where domain knowledge is irreplaceable. The full source is on GitHub .…