It might also be the reason why life seems to speed up as we get older. When we're in our teens, there are a lot of firsts, while firsts at fifty are rarer.
To paraphrase one of the greatest philosophers of the twentieth century, Winnie-the-Pooh: you don't know you are making memories, you just know you are having fun.
Episodic memory covers the personal, unique and concrete experiences we can retrieve from our own past. Semantic memory is timeless knowledge that we share with the world about the world.