Problem discovery is a challenge that every founder will face. How do I find a problem worth solving?
You're not going to discover a problem worth solving by fantasizing with a cofounder along the lines of "wouldn't it be cool if there was an app that…" and you're not going to discover a problem worth solving by playing the this for that game.
However, here's one way that will definitely work:
Do Something Mundane!
Go and perform some mundane task that normal people around you are doing every day. The choice is endless. Here's a few to kick things off:
Here's the important thing. The point of this exercise is not to create a startup that solves the task as a whole. The point is that by performing a mundane task you will uncover an inefficiency at some point in the process. A "how do I…?" moment. How do I promote what I'm selling? How do I know if the company I applied to has looked at my job application? It might be just a small part of the process, but it might just be a big enough pain in the ass that someone will pay you money to solve it for them elegantly.
For a startup, that's an excellent place to begin.