The basic idea is that people open up to feedback far more if you start by complimenting them (slice of bread number one), then you give them the difficult message (the shit), then wrap up by reminding them how much you value their strengths (slice of bread number two). The shit sandwich also has the positive side effect of focusing the feedback on the behavior rather than the person, because you establish up front that you really value the person. This is a key concept in giving feedback.
