Courts will sometimes make assumptions when it comes to child support payments and the amount that needs to be paid by each parent. While these may be an unavoidable part of the process, it can be argued that assumptions don't always tell the whole story.
For example, imagine that one parent has sole custody of his or her child. The court is then going to ask the other parent to pay child support, which is intended to be roughly half of the money needed to raise the child. The parents are supposed to split this cost, just as they would have done if they'd stayed married.