It's where you write down what works and how you achieved it. So times he has really opened up to you look at the situation you were in and what you did to allow that to happen. Also, you can look at times when things didn't work and do the same. It is really good at identifying positive things and sometimes you can find a theme. I've found it really helpful (although it is a bit like homework :-)
Great job on the not asking what he was stressing about - I so would have tried to extract more from my h!