It is a common problem. I think it comes from you, the builder, having spent thousands of hours on a problem (here making an electronic diary) trying to get in

It is a common problem. I think it comes from you, the builder, having spent thousands of hours on a problem (here making an electronic diary) trying to get insights from someone who have just spent a short minute thinking about the same problem. Instead of thinking about it as "talking to your users", try to think about it as observing how your product is used, and how they work in general within the domain. Observe them directly if you can (sit next to them and just watch them do their stuff), or indirectly e.g. by extensive application logging or maybe a screen recording tool (like hotjar).