Don't be upset with that .... unless the person has forgotten it is your birthday or anniversary!!
An article in Mint states that neuroscientists say forgetting is crucial to the efficient functioning of the mind, to learning, adapting and recalling more significant things!!
I guess you could liken the brain to the computer. If one is to keep all the files, pictures, songs, movies... and continue to add more without deleting what is not required, the system will definitely slow down. Here, one could back up on a CD or add more memory but alas, this is not the case with the human brain. It is thought that if one has to remember all that has happened and store it , it could possibly drown you in a sea of inefficiency.
It is true that unless an event has made a lasting impression on the brain it probably would not remain in the memory. Trying to remember something that has been forgotten may revive some impressions and like a jigsaw puzzle may have the pieces, but in the wrong places!!
Most people fail to register all information at a time. In an experimental process when respondents were asked to focus on a particular activity, other happenings in the same sphere went unnoticed - a phenomenon labeled as “change blindness”.
Forgetting, strangely is a very active process, although subconscious. As the brain stores a small piece of information, it is at the same time erasing large amounts of irrelevant matter so that it can free brain power for more important issues. Mundane, every day matters are not considered important to be stored.
So, if there is an event you want to remember, ensure that you keep a journal with atleast some tab to associate it with. Photographs are also memory jogs.
If you have to appreciate why it is important to forget, I would need to quote James McGaugh one of the world's leading experts on how the human memory system works, who says Remember that forgetting can be very useful, : “If you used to go out with Bob and now you’re married to Bill, you want to be able to say, ‘I love you, Bill.’ That’s why forgetting is important.”
Moral: Remember to forget and do not forget to remember. And you have to remember what to forget and at the same time not forget what you should remember. Good luck!