One of the first principles I learned at "Coach School" was the importance of being non-judgemental.
This is a difficult skill to master. It's our natural tendency, when meeting people and discovering things about them, to build a story around how they came to be and then to form our own opinion about it. And there are a number of problems with this.
Here are a couple:
Firstly, the stories that we build are at best incomplete, and at worst can be completely inaccurate. We make assumptions that can be way off the mark (e.g. that guy's not smiling so he must be a grumpy so-and-so).