Sometimes you remember things. Long forgotten things. Things from your childhood. Things from the time when you had just started making memories. And you remember them and may be smile or frown at those memories. And may be you are the only person who still remembers those moments. There may be many people who were part of those events but it is unlikely that anyone else would still have a memory of that event. Does it make those events less real? Did they actually happen?
There are events that have left behind proofs that they happened. So we know that Titanic sank because of all the documented proofs. Newspapers, living testimonials, physical evidences, newsreels etc. And then there are things which can be inferred. So we infer that dinosaurs were wiped out by a meteor by the geological evidences. And then there are things which only exists in the memory of one person. Do you remember the time when the girl you had always liked sat next to you in the bus and talked about how bad her work is? Do you remember when you raced your father every morning when he dropped you to school and every time you won? Did it really happen? Or is it something that you just made up? Where is the proof?
Those events exists only in your memory and once you are gone, those events are gone too. They never happened.