Why do kids say "Hello" ?

After you've been a teacher for a while, you start knowing more and more kids. You start seeing former students around more often when you are out and about. When you see a former student, let's say at a sporting event or grocery store, there are only two things that could happen: 1. the student says "hello" to you. or 2. The student does not.  So why do kids say "hello"? What moves them to walk up to you, as their former teacher, and say hello? In some cases, you could have been their teacher 15-20 years ago, yet they still say hello. So why? Well, it certainly isn't because of what you taught them. Former students do not come up to me and say "hello" to me because I taught them what a Ziggurat was during our Mesopotamia unit. Former students say "hello" because of how you made them feel. Because how you greeted them each day. Because of how you answered their questions. Because of the experiences you created for them. Because of the atmosphere of your classroom. Because of how you pushed them to reach their potential. Because of how you gave them self-confidence. Because of how you created a safe environment. Because of how much you cared. 
The position we are in to make an impact is such an awesome responsibility, so make one! 
After years and years and years and different teachers and different people and different experiences in their lives, for a human being to come up to you and say "hello" after all that, I'd say you made an impact on that life. Well done.