We covered this in my PD class too... what we came up with was something along the lines of this:
When you are young, your parents hold responsibility for your H, and as you grow up, you should start taking more and more responsibility. When you're old, you will need others to help keep you Hy, but throughout your life, there will always be someone else sharing the burden - sometimes you'll be independant, and sometimes you'll be dependant.
It really depends on eash individual though... some people are just not capable of looking after themselves, i.e. some people with disabilities, diseases or injuries cannot care for themselves, and their H will always depend on someone else...
Hope this helped