A more thorough explanation:

Definition: Unfit, adjective, means not suitable or qualified for a particular use or service. For example, if you buy a product that doesn't work properly, you can return it to the seller because it is unfit for its intended use. In family law, unfit means morally unqualified or incompetent. For instance, if a judge finds that a mother is unfit to take care of her child, the father may be awarded custody of the child because it is in the child's best interests.

• The shoes were too small and unfit for walking long distances.
• The car was sold as new, but it had many defects and was unfit for driving.
• The court found the father unfit to have custody of his children because he had a history of domestic violence.

The first two examples illustrate the first definition of unfit, which means not suitable or qualified for a particular use or service. The shoes were too small, so they were not suitable for walking long distances. The car had many defects, so it was not qualified for driving. The third example illustrates the second definition of unfit, which means morally unqualified or incompetent. The father had a history of domestic violence, so he was not qualified to have custody of his children.