Reality sharing is complex but not impossible.

The setting for a shared reality. Trust is a major factor, being able to trust, being trustworthy. 

Next is the quality of the reality. Different people have different needs to consider calling something real. 

Trying to create an environment that cultivates reality sharing. 

Talking to the lie. Accepting a person's lies to help them live within the reality they have for you can facilitate getting to the topics that need to be resolved. Like why they need to lie. Most relationships don't get past this phase. It is such a rare occurrence, I think the average human life span isn't long enough for most people to come to terms with themselves.