Just watched this, and see a lot of reviewers who are baffled by it. But by the end, it became quite clear to me what the intent was with this film, and I endorse the wisdom it attempted to convey, because it lies at the heart of everything else in human reality. It's actually quite simple in concept, but complex in practice and comprehension due to all the noise that plagues our existence. At its core, "Flashback" represents our power to choose, and the trappings that spawn from those choices, as well as the choices of others. But it suggests, rightly so, that we aren't as bound by the limitations we perceive are imposed by those choices as we tend to think.

In fact, we can choose to reprogram ourselves any way we want at any time we want, and choose a different mindset. We are not a product of our past, nor of the conditioning of our upbringing, or of the dreams and wishes of our parents, the rules of society, etc. We, and we alone as individuals, have the power to choose how we think and feel and act. Circumstances and other people can’t choose for us unless we let them, but choosing to let some of them do so is also a valid choice, as long as it's a conscious choice.

And yet the vast majority of the population live their entire lives ping-ponging around off all of those barriers, those walls, letting everything else shape who they are, how they think, how they feel, and therefore how they act, without realizing, or perhaps only catching glimpses, that they're the product of those mechanisms. Which in turn extends those conditions and limitations onto others.

The movie conveys this several ways, one of which toward the end is by associating images of the "big bang" (the birth of the universe) with Fred's mother (the "lifeform", as the message across spacetime tells him, that's imposing its will onto him), with his personal "big bang" (Fred's individual birth), and up to that point throughout the story by disassociating time and parallel timelines into an infinite "now", which represents our power of choice that we only think we're engaging in, but that most of the time isn't really our choice at all.

It's about waking up to the fact that nothing else has power over us unless we let it. We’re in charge of our own programming. Concepts such as "groupthink", "confirmation bias", "ideology”, "religion", “tribalism”, "belief", etc. all stem from this core conceit.

Never believe. Always question. Rebuke belief, a.k.a. bias, a.k.a. groupthink, a.k.a. ideology, the bane of skeptical, logical reason.