I once told an author that he needed to include "more concrete and fewer roses" when writing a scene about his past. When we talked about that, he was kind of frustrated with me - because when you're writing about your past, it usually goes through filters - but when he read back through the scene (having taking a few weeks away from it) he started to see what I meant.
You see, there are a lot of rose-colored filters that smear Vaseline on the edges of your memory and make things all soft and pretty.
There are even more - at least for some people - that make all of the memories gritty and dark and film noir.
Unfortunately, neither of those sets of filters really give a true version of what went on.
Don't get me wrong, here - I'm a firm believer in the fact that we are all telling stories when we talk about the past. There's a line from Thornton Wilder that goes something like "the future is always the same, but the past is always changing, because humans can never agree on it." And I truly believe that. Even so, I think that if you tell people that what you're presenting for them is The Truth, then you need to get as close to that as possible.
I'm sure there are people who would say differently, but I see Biography and Autobiography as genres where you have to really tell the truth. Memoir, on the other hand, can be a little more flexible. And Creative Nonfiction... well... that's just a whole other world of its own.
For the most part, when people are telling stories about what they did last weekend, or what their prom was like, or what - exactly - they said during their proposal, that tends to be more Memoir than anything else. It's a desperate attempt to be correct, but also an attempt to tell an interesting story. This means that some details get left out in favor of more relevant points. And some gain prominence depending on the latest audience. And - from time to time - you have to "Be Ready to Kill Your Darlings."
For an explanation of that reference, I offer you a blog post by "The Everywhereist" - quite possibly one of the best "travel" blogs on the Internet. Thankfully, she only seldom writes about editing. Otherwise, I'd be out of a job.
Enjoy (and possibly follow her regular blog while you're there - if you generally like my sense of humor you'll love her blog): http://www.everywhereist.com/writing-a-memoir-be-ready-to-kill-your-darlings/