The need to maintain an effective focus spans both individual mentor conversations and the overall assignment. Mentoring does not happen in a vacuum, it happens as part of real life. Mentoring assignments often begin well (helped by enjoyable discussion of intentions, goals and a general sense of optimism). They then continue against a backdrop of everyday events, challenges and change. These unexpected elements may then cause the conversations to shift emphasis, or alter in nature.
These natural developments require you to keep sight of the overall intentions of the relationship, while staying flexible enough to navigate effectively as circumstances change. As a mentor, you have a balance to maintain: You want to maintain the relationship with the mentee, and you need to keep sight of the stated goals of the mentee and encourage awareness of those. You need to be open to adapting the focus of the assignment if that is appropriate.