Does it ever happen to you that someone tells you something, then weeks or months pass, and the same person tells you the same thing again forgetting that they already told you before?

Why is it easier for the listener to remember than the speaker?  Is there some fundamental difference in the way memory operates?  Or is it that the memory is more evocative for the listener just because the fact being told is uniquely associated with the teller?  For the person doing the telling you are just a generic listener.  Or is it something else?  Answer below.

None of the above.  There is no evidence of any asymmetry here.  Its pure sample selection bias.  Each party is equally likely to remember the first event but the mirror-image events in which the listener forgets being told and the speaker remembers telling never happen. Because the speaker wouldn’t repeat it if he remembers telling it the first time.