Keeping the Mediator from Making Assumptions about the Parties

This Saint Patrick's Day I had a good reminder that a mediator should never make assumptions about matters such as culture, experience or sophistication of the parties before them.  The case was brought by a Japanese man who had sued his former employer, an American company, for wrongful termination.
The Company's representative, a jolly Irish gentleman, was respectful of the process and greeted the Plaintiff warmly at the outset of the hearing.  At the end, I said to the Defendant that I thought it unfortunate, but that the genesis of the conflict appeared to be a breakdown in communications at the workplace, as so many employment matters are.
It was at that point that the Irish Defendant muttered something to me in perfect Japanese!  It turns out he had lived in Japan in his youth and had a great respect and deference for the people there, whom he considered family.  Had we not engaged in that banter, I would never have known that this individual had such a deep understanding of the Plaintiff's culture.  What was more, he had been a party himself to a published lawsuit many years ago, and knew the vagaries of litigation firsthand.
I was reminded of how important it is to enter every negotiation fresh and engage in basic conversation at the outset in an effort to ferret out the keys to helping the parties arrive at a mutually acceptable settlement to their disputes. How do you keep yourself from making assumptions about the parties?