From Chapter 7 of There Are No Secrets by Wolfe Lowenthal, thoughts on why to thank a difficult, troublesome person:

... No matter how hard and unyielding our opponent, our inability to gently deal with him is indicative of our own stuckness. It is the exploration and eventual dissolving of the stuckness — not winning — that is the point of push hands. The "game" we really should be playing is with ourselves; we are coming face to face with the physical expression of the issues we hide from in our lives. In this confrontation with the self there lies the possibility of progress. We thank our opponent for providing us with this opportunity. If we really understood K'e Ch'i we would bow to anyone who "pushed our button" rather than become angry.

_{(cf. Gentleness, Sensitivity, Compassion (2014-03-09), Virtues of Softness (2014-03-20), Good Manners and Taiji (2014-04-03), ...) - ^z - 2014-04-15}