Craft: On Writing Descriptions of People

I was having a brainstorming session with my crit partner months ago and my delay in writing this post is equally long, but I wanted to finally get this out.  

Following said mentioned brainstorming session I remembered a little #editortip from Adrien-Luc Sanders. To quote:

Think of people who've made an instant impression. Most compelling trait? Probably not their eyes.

Those 2 sentences and 1 question stuck with me long after reading them. Then I had to know: How do I look at people? What's the thing I notice first or look at first when meeting a new person? For me it's the traits I like least about myself, for others it may be what they are attracted to the most. Each person is unique in their personalities as well as what they are drawn to.

So, why is it we're all after the eyes. Is it the easiest to write? The most common feature? The windows to the soul aspect? The final question you have to ask each of your character's is: Do you really look a person in their eyes first? And go deep. Dig into your character and put yourself in their shoes. Are they shy? Then probably not the eyes, probably the shoes or the scruff on a chin would be the first thing they'd notice. A tall person might find more interest in someones hair or their shoulder's, especially if their are around a lot of folks a bit smaller then themselves.

Bottom line is that by using their observances of other people around them you can show certain aspects of their own personality versus telling the readers.

What do you think? Is it easy or hard to focus on different descriptors to lead the view one character has on another?