What does "just can't" mean, exactly? Just curious, because I felt that way, too, until I had a newborn and was forced to wake up with less sleep and discovered it was physically possible. Still felt awful all day, but it was possible.

Moreover, when I sleep more, I notice that I'm sharper and I find it easier to take on tough challenges: this means that sleeping longer makes me happier for the rest of the day. So I'm also willing to live a tougher life. So there's also a trade off with: yea, you have less time, but the less time that you have, you're happier. Or at least, that's my experience.

And not only are you happier, you're also more capable. So it's more easy to live according to your own rationality and it's easier to not live according to your emotions and instincts.

Again, just my experience.