Always Judging by the Cover
I regularly find myself judging people in the first few seconds of meeting them. I don't want to, and I know it's unfair, but my mind immediately places them in a category that fits my preconceptions.
Teachers use to encourage us not to judge a book by its cover. Maybe it's because our books no longer have covers; they live in screens and we can read 1,000s of reviews on Amazon before we open the first page, but you don't hear that saying much today.
Even if it doesn't apply to "books" anymore, let's remember to look past the cover when meeting someone new. Let's not judge a person upon meeting them, in the first week, or even the first few months of knowing them. Some books get better after the first chapter, and sometimes you need to walk with people for a time before you realize you're not all that different.