Sometimes, there are challenges. The most common problems arise through poor communication, through not monitoring progress or not managing timelines appropriately.

As a supervisor, you'd need to keep your eye on the "getting the PhD".

If you see problems happening at any stage, don't let them drift. Have conversations with the student. Talk to people in the co-supervisory team. Talk to your mentors and people in the university, in the Graduate School, in the Doctoral Academy.

Don't let a student drift, because you don't know how to address a particular challenge.