I think problems in any of these areas can often be reflections of ourselves and our own lack of self discipline. What we perceive on the outside are often manifestations of internal issues. It's easy to give into temptation, particularly if tired, weary, etc which can give rise to bad and unhealthy habits. That reduces self-discipline and makes it less likely we will achieve our goals. By caring for our basic needs, health, rest, etc, we nurture our ability to be self disciplined in any or all areas of our lives.