Wands choose the wizards. And to some degree, your niche chooses you. The tech stack I built for video games: gcloud, chromeos, android vulkan, admob. Is essentially a "native mobile ads" platform.

It was only when clients requested I serve ads that I realized what I had built!

Now it unlocks free cash flow potential. And I'm working on my own private buyers list, inventory management, real time bidding exchange & auction tech ;)