A startup's initial problem is usually what the product should be and how to get the first users. It may sound like those are two problems, but they're not. Ideally you solve them simultaneously, and the process of trying to get users shows you what the product should be.
paulgraham.com • How to Get Startup Ideas
Brian Balfour • Building a Growth Framework Towards a $100 Million Product — Brian Balfour
Paul Graham suggests that generic launch can be a solid start for the same reason. Get your product out there, see who seems to like it most, and then reach out to those types of users for deeper learning.
Rob Fitzpatrick • The Mom Test: How to talk to customers & learn if your business is a good idea when everyone is lying to you
Paul Graham • How to Get Startup Ideas
The essential task in a startup is to create wealth; the dimension of wealth you have most control over is how much you improve users' lives; and the hardest part of that is knowing what to make for them. Once you know what to make, it's mere effort to make it, and most decent hackers are capable of that.