Working a job that involves interacting with customers all the time can be incredibly draining. You're forced to put on a friendly face even when you're drained to the bone, and lots of people can be incredibly boring or annoying.
Luckily though, there are the few and the rare customers who make working with the public worth it. The people with stories wild enough you could listen to them talk for hours, or the intense vulnerable moments that sit with you for years.
I work in a library. One evening a man, perhaps 70, came in with his two grandchildren, maybe 5 and 9, and headed over to the children's section. After a while the man approached me as the kids browsed the shelves, and asked: "I was wondering if you could find us a book, if there is such a book..."
And as he said this he trailed off and looked away. After regaining his composure he continued, sincerely and warmly: "See, their parents both died in an accident abroad, they were on vacation. Now I have custody of them and I have absolutely no idea how to talk to them about it." This I will never forget.