The problem with "when hungry, eat", is that hunger is not really a good indicator for sustenance needs for humans. Living in western countries, we are surrounded by easily obtainable and addictive foods and nutrients. If we let hunger control our eating, especially in this kind of environment, most people tend to over-eat. Combined with recent results that caloric restriction and potentially intermittent fasting may be very healthy choices, I think it might be likely that hunger is really a maladaptation in modern society.

I do fully agree with the part "When tired, sleep". Unfortunately it is very hard to apply if I also want to maintain a working home-life with a significant other that has a different sleep-pattern.