Latin pater (“father”) → patronus (“protector/patron”) → Old French patron (“model, exemplar”) → Middle English patron/pattern → modern pattern.
Originally, pattern meant something like “an example, model, or template from which something else is made.” By the 1500s, it expanded to mean a repeated decorative design, and eventually to the broader modern sense of a recurring arrangement or regularity.
So when we say “I notice a pattern,” there’s an interesting older idea underneath it: you’re recognizing the model or form that keeps reproducing itself.
And patron and pattern are historically the same word that eventually split into different meanings.