This is a surprisingly useful exercise. I'm surprised nobody does this IRL.
In this exercise, you don't have to be an expert in any field (but it helps a lot). It didn't take a genius to say, "Uber for people's houses" to get Airbnb. It didn't take a genius to say, "books on the internet" to get Amazon. But it did take massive amounts of hard-work and good decision-making skills to transform those companies into the behemoths they are today.
In a lot of ways, this is the opposite of Elon Musk's "First-Principles Thinking". With First-Principles, the goal is to distill a single problem into its purest form. For instance, to ask "How cheap can rockets feasibly be?", you have to understand propulsion and money and physics and space and materials and government-regulation and so-on and so-on.
It's a practice best-suited for geniuses who have the skill to do the stupid thing, and industrious idiots who don't actually know how hard it's going to be to do the stupid thing. And it's even better if you're smart enough to know how to do it, but too dumb to see how difficult it's going to be 💁
Just a tip: make sure to include at least one wild-card!
Introducing some entropy into the system with topics like "hedgehogs" or "noodles" or whatever will keep the creative juices flowing!