Why do mentors need an induction and mentees a briefing?

For example, mentors who have not been induced often tend to spend far too much time talking and not enough time listening. Broadly speaking, where neither mentor nor mentee is briefed in their roles, only about 30% of relationships deliver significant learning. Where mentors are trained, the proportion rises to about 60%. Where both mentors and mentees are briefed and supported afterwards, the proportion rises to around 90%.