Generally the only reason they would not reveal something in a "regular discussion" is that you're not asking the right things. Try asking open ended questions, such as:
1) "What’s the hardest part about      [problem context]    ?"
2) "Can you tell me about the last time that happened?"
3) "Why was that hard?"
4) "What, if anything, have you done to solve that problem?"
5) "What don’t you love about the solutions you’ve tried?"

People are more comfortable talking to someone like themselves: Don't go overboard, but don't be from another planet.

People are more comfortable talking to someone with whom they have a rapport. Don't just jump right in to questions, ask them some background questions first and maybe give them some of your own background to instill more of a sense of trust and openness.

To glean further 'hidden' insights from them, if you have a software product, you can record their exact on screen interactions via services like Lookback.io That way you can see hesitations, confusion, etc. You could then ask somewhat targetted questions about things you notice in individuals, or things you notice as a common theme across individuals.

If you have a hardware product, you could possibly videotape someone using it for the first time.

If you'd like tailored advice to your specific product let me know,

best,

Lee