Of course we take it for granted, like all things in our senses it becomes normalized, dull, repetitive. That's just part of our survival instinct, when we get to a "safe routine" and can expect where to regularly sleep/eat/not feel threatened, then the arousing part of it all goes away. That's a drastic oversimplification of course, and meanwhile our natural urges will drive us to seek out other things as we fill that time (sex drive, competition, territorial, socialization, expand and learn from culture etc, further dominate our environment if at all possible).
It is crazy because there is nothing else to relate it to, except perhaps sleep, altered states of mind, and I suppose memories (particularly distant ones, however relevant those are). And yet it is only sometimes good, and sometimes unbelievably bad, and many of us (even a tiny sample like just those reading this forum) can have drastically different overall experiences in such a manner. Some people have decent middling lives, some are amazing, some know only pain and loss..
Anyway, I think a defining moment for me was probably a couple of decades ago, watching a short film or something with the abstract comedian Steven Wright, and he put it this way basically:
Before you were born, there was this unknowably long time where everything else existed except for you - and then you came into the picture. You grow up, have your life for however many decades, and then you are gone. After that, there is still this immeasurable amount of time that will pass. Essentially, you're entire existence is just the merest blip, with infinity preceding it, and another infinity after that blip.
...gah. It kind of gives me the chills to think of that. It really makes your life seem so incredibly important, and so absolutely useless and inconsequential at the same time.