This is a great blog post by Tim Challies in which he poses a great question from a book called True Friendship. In the book, the author states that he wants his true friends to ask the tough question of:
If you were the devil, where would you attack yourself?
It is a great question that is proactive in anticipating my areas of weakness, calls me to identify my vulnerabilities, and lastly and most importantly involves that brother in strengthening me. This is true discipleship in helping a brother grow in holiness and I hope my good friends seek to ask this question of myself so that I can give God the glory during my walk.