I thought this was obvious, as well as something that has been researched and discussed before.... A simple example of this is falling asleep. We can't remember the exact moment we fall asleep because our conscious perception of things (really just a sort of feedback mechanism) is last in line. We're already out by the time our conscious perception of falling asleep would have recognized it. Another example is our body craving specific nutrients. By the time we consciously realize we're hungry for something specific, our body has already been craving it for some time, and even then we still don't always make the connection that the craving has something to do with nutritional requirements (it doesn't always of course). And when we go get food, it's because we're mentally or physically hungry, so it's an inevitability. Much of our actions are just reactions. If we were truly conscious of things all the time and consciously made decisions about everything, we'd likely make a lot of the wrong decisions and we'd get frustrated with the sheer amount of information and tasks we'd have to handle while being painfully aware of every mundane thing we do. Ever try suddenly putting conscious attention and effort to something simple you do regularly, and find yourself confused for a moment? It's much easier for us to put things on 'auto-pilot', use 'muscle memory', and consciously tune out if it doesn't actually need attention or focus... but that has the consequence of leaving us less aware of everything we do, unless of course we make a conscious memory of it.

Edit: Had started writing more but had to go do something, and now I've forgotten.