Sometimes this is given by attribution as when parents continually give the message that the child is not strong.  Or if the family model being sick is how we are and survive in the world.  A lot of alcoholic families hold this injunction within their system and individuals even if not addicted themselves find others ways to be not okay.  As they do not know how to be any other way or what emotional or physical stability may be like.  Here emotional drama , destructive or co-dependent relationships may be how the not being well or sane is acted out.  In other cases it is were the child has got stroked from being unwell a way of getting attention that worked.  Parents that are busy people that may have love but no energy for their child.  When the child is unwell the attention that is yearned for is received.  This is stored in how to be and there is a strong investment in this role and a fear of moving out of it in-case one does not get want they need as an adult.  People can act this out in the health service with those that are constantly being attended to in some way shape or form.