This is more abstract rather than a proper example.
Let's say I have a vague idea of a problem, but nothing concrete, just that someone is unhappy with their current circumstances. How do I go from vague to knowing what the problem is, all relevant context, and what the customer's results are now and what they want?
I'd just love some resources which gives me a systematic way of doing this. Thank you.
I'd say find these people and try to talk to them.
A bit more context/niche would indeed help. But I think the first step would indeed be to go out there and observe, get to know the situation better. Reality can often be different than what we assume.