Brass alloys weren't formed out of pure luck. Prior to the first millennium, brass was already being produced by man, but the procedures were primitive at best. The difference in the melting points of copper and smithsonite, also known as zinc spar or zinc carbonate, made it possible to create brass but primarily for decorative purposes.
It wasn’t until copper and zinc were viewed as separate metals did the quest for discovering alloys took off. By the Industrial Revolution in Europe, brass increased in demand. Brass plates provided materials for applications ranging from shipbuilding to agriculture. Still, virtually nobody bothered to ask why copper and zinc made the perfect pair.
To understand this, it's important to look at brass from a molecular point of view. There are two ways for alloys to work: swapping out some atoms or occupying the gaps between atoms. The phenomena gave birth to substitutional and interstitial alloys, respectively. Brass is the result of the first process, while steel was produced through the latter.
Substitutional alloys are only possible if both metals' atoms are roughly the same size, inherent among d-block metals or transition metals (except lanthanides and actinides). Copper and zinc, in the periodic table, sit adjacent to each other, with zinc being slightly heavier. Depending on the amount, zinc may replace as much as 35 percent of copper's atoms.