Threads like this, or topics like this, seem to have an attitude of Positive Thinking With Norman Vincent Peale, you know, "If you believe you can do it, you can!" Like I THINK I can climb Half Dome; and if I fail to do so, well, I just don't have sufficient personal discipline. It can get cruel, quickly, to have these (unbiblical) expectations of people.
While I agree with your general concern that people are different and that there are no "cookie cutter" solutions the above statement is patently absurd.
Can you cover a marathon distance in a day? I don't know the answer to that question. Maybe you can.
I know, right now, that I cannot run a marathon but having
trained for and completed five marathons I know how to train my body for one.
The first time I flew the the Far East and back I was wrecked for a couple of days in terms of sleep and exhaustion. After living there for 3 years and having to make that trip a number of times my body became accustomed to something that was very hard on the system the first time.
When Paul says that he disciplines his body in 1 Cor 9:27 to control its lusts then this is not "positive thinking" but training.
Yes, I agree, let's not make hasty generalizations (which I have not) about whether or not some people may require more sleep than others but let us not likewise compare the training of the body to the power of positive thinking.
My experience is that many people assume they would be non-functional without a certain amount of sleep precisely because they always get a certain amount of sleep. It's pretty hard to put that to the test if the person is both out of shape and never has, for an extended period of time, tried a different sleeping pattern.
I'm not arguing for any ideal number of hours of sleep. I'm not telling people to go out and tell people they're lazy. I'm simply making a broad observation about an ability to train the body. Whether or not what we may become accustomed to is good for you is another thing. I once went an extended period of time getting 3.5-4 hours of sleep a night and drank too much coffee as a result. I thinnk it led to some unheatlthy mineral deficits and I used to wake up with the worst kind of muscle cramps.
Lately, I've generally settled on about 7 hours of sleep as feeling really rested but I usurally get 6. Last night I got 5 and I'm functioning fine. I'd like to take a 15 minute nap right after lunch but, alas, no cot nearby. Sleepiness for me is when I get up earlier than I'm accustomed. It seems to matter less that I got 6 hours of sleep and woke up at 5:30 than if I get 7 hours of sleep and wake up at 4. It's the getting up at 4 that makes me more sleepy later in the day.