One research idea links it to a feeling of familiarity that appears without an accessible memory of its source. A detail in the setting may remind you of an earlier experience, but you cannot retrieve the episode itself. Another line of research looks at how we check a memory signal and notice a mismatch. Neither account explains every case yet.
Laboratory experiments help researchers study individual mechanisms, but they do not reproduce exactly that brief, unexpected moment in a café. So a confident answer such as “it always happens because of one brain error” would sound more certain than the evidence allows.
Déjà vu can be an intriguing experience, but it does not prove that you have lived this day before, and it does not predict your next conversation. Sometimes it is enough to notice the contrast between familiarity and novelty. A minute later, the light in the café is still the same, but the feeling has passed; the moment continues without the mystery.
The stars speak. The choice is yours.