Event Segment Count Higher at the Unique Visitor Level than the Visit Level

I created two separate segments, one where a custom event exists at the Visit level and one that exists at the Visitor level.  When I apply each of those segments to their respective metric (Visits & Unique Visitors), the Unique Visitors count is higher.  How is that possible?  Shouldn't the event count at the Visit level be greater than the Unique Visitor count?