You two may have a hard time when it comes to growing as individuals within the friendship. Your friend will be on a highly emotional path toward self-knowledge during this friendship; they'll be doing a lot of hard work and personal transformation. You'll have two different ways of meeting personal growth issues; you'll be polarized between the mental (you) and the emotional (them), and neither of you will understand where the other is coming from.
Your pal will tend to project their subconscious need for change onto you. While this should be a personal process, instead they'll try somehow to change themselves through you. You two might have a hard time getting along as a result, especially if you start putting each other on the spot about your beliefs and trying to force a defense of the qualities that make you who you are.