Most of parents including the author of the present book not always manages to achieve obedience.
But if we remembered that children want to help us and to be useful, we would not do unpleasant duties of house instructions and would not give instructions, being in bad mood.
You cannot wait from the child of constant responsibility for performance of the duties, even in years.
Adults sometimes too are irresponsible.
The child needs to remind.
Try to show a maximum of patience and to do reminders in a polite form, selfevident tone as though you spoke with the adult..