To act as the instigator, catalyst, or motivator that compels someone to do something or causes something to happen. While they haven't admitted why they reversed their decision, everyone knows the lawsuit served as the driving factor. The willingness of the banks to let anyone and everyone get a mortgage, whether or not they would be able to meet their repayments, served as the single biggest driving factor behind the financial crisis. My family has always served as the driving factor behind me.