By and large I agree with this, but I think there is another element to consider, which is your overall energy levels. If you exercise, eat right, laugh, spend

By and large I agree with this, but I think there is another element to consider, which is your overall energy levels. If you exercise, eat right, laugh, spend time with family and friends, then you're more likely to be able to consistently put in this kind of effort. I don't think you can or should aim to do much more than 4, but I think a very large proportion of the world isn't capable of even coming close to 4, because they don't or can't manage their energy effectively. I also agree it is possible to do longer bursts, but that is pretty rare in my experience.