How does MVC know which route should call first?

public static void RegisterRoutes(RouteCollection routes)
       {
           routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

           routes.MapRoute(
               name: "DefaultOne",
               url: "{controller}/{action}/{id}",
               defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
           );
           routes.MapRoute(
               name: "DefaultTwo",
               url: "{controller}/{action}/{id}",
               defaults: new { controller = "Patient", action = "Index", id = UrlParameter.Optional }
           );
       }