How do we distinguish between hardship (mashaqqah) and harm (ḍarar) concerning obedience to parents, especially since obedience to them is not obligatory in matters that would bring harm upon the child?

Obeying any commander is never devoid of hardship, and the human soul inclines towards ease. If a command goes against one's desires, the hardship increases. Obedience to parents is obligatory, even if it involves hardship, unless the hardship increases and turns into harm. In that case, obedience is not obligatory. Harm is excessive hardship that is usually difficult to bear. Defining a clear boundary between tolerable and intolerable hardship is difficult, as it varies among individuals, circumstances, and customs. Islamic law considers great and excessive harm obligatory to remove, but it does not prevent slight harm. Islamic jurisprudence relies on custom and tradition to determine the harm that must be removed.