Falling into the secondary.

> Mihu had a monk ask Yangshan, "Do people these days need enghtenment or not?" Yangshan said, "It's not that there is no enlightenment, but what can be done about falling into the secondary?" The monk went back and reported this to Mihu. Hu deeply agreed with this.

My question is simple: what is primary such as that it could permit deviation and what is secondary such as that someone could fall into it?