for what reason might someone decide to bring a civil law suit against a person or a business? what might the
consequences be for filing suit against someone you know and work with?

The reason for a civil law suit can be almost any harm or wrongful act done to an individual or business, by another person or business entity. For example, a breach of most contracts can be considered as the reason for a civil law suit. Also, car accidents and misfortunes take a big share in civil law suits.

If a defendant loses in a civil law suit, he usually pays in dollars, as reimbursement for the harm done. Rarely, this results in actual time in prison (behind bars).

Usually, when harm or potential misunderstanding includes someone you know or work with, the first step is to try to settle things without court. Legal costs can become overwhelming, especially if the problem could be solved beforehand.

Also, the social and relationship aspect is extremely important. If you take a case to the court (especially if the reason is minor and could be potentially settled without the aid of legal entities), the relationship between you and the defendant will always have a hostile notion to it. That is a factor to take into consideration if the defendant is an acquaintance or co-worker.