Fact
Deja vu may be a memory system checking its own work
The feeling is not that you remember. It is that you feel you should.
One leading account holds that deja vu is a false alarm from familiarity detection, firing without any actual retrieved memory. Another suggests it is the brain noticing a conflict between systems and flagging the error – which would make it a sign of memory working, not failing. It becomes less frequent with age.