Lucky First I asked him to say intuitively on which side he would block. He chose the marked move in the diagram. The reason is that if White plays the common joseki then the a point is not so interesting for Black.
(So I was wrong :-) )
Lucky If White blocks on the other side then a is a very good point for Black. This is the first thing that comes to mind.
Lucky Then we looked at other possibilities. If White wants to play first on the left side then she should accept some loss in the corner, by playing 2 here. This is reasonable.