Personal gain at play!
Person knew there was a rule and he/she knew she broke it, but that suited him or her just fine. Actually the situation could be all too common: a person leaves work early because he had to attend a meeting at the school of his kid. But by doing that, he left his co-workers with a problem of one hand shorter. Sometimes it is possible to get work done quicker and simpler, or to get a kick, by not following the rules. Smoking were it is clearly not permitted for example.
Bonusses focussed on performance, or unclear communication of the organizations goals can contribute to this type of violation.
Although we would hope you would never have to experience this, it could be worse and count as a case of sheer recklessness. Driving at ridiculous speeds. Clearly and blatantly ignoring safety rules to show off