Common No Longer Goes With Courtesy

I was in the pharmacy getting medicine for my high blood pressure.  While there, I picked up some other items and headed to the checkout.  The lines were rather long for this pharmacy this time of the day, and I soon found out that the computers that handled debit and credit cards were very slow, and those that handled the checks weren’t much faster.
As I waited in line, I noticed a woman juggling several small items, obviously trying to not drop one of them.  If she would have dropped any, she wouldn’t have been able to pick it up due to the continued need to juggle the rest of the items.  She also was nervously looking at the clock.  I could only imagine that she had some place she needed to be, and was concerned about getting out of the store in time.
My line went faster than hers due to several cash customers ahead of me.  I wasn’t in a hurry, so I told the woman she should go ahead of me in my line.  She thanked me profusely and stepped into the line.  It happened that as she was paying for her items, I also was able to check out at another register.  The clerk, by the way, thanked me for allowing her to go ahead of me.  I went near her, placed my hand on her back as she was leaning over, and said, “Have a good day, ma’am.”  She thanked me again and we parted company.
Why is it that we feel so good when we do something like that, and why is that kind of thoughtfulness so hard to find sometimes?  It makes everyone feel good, the clerks, the giver, and the receiver, and costs nothing except a little time on my part.  I rather imagine I wasn’t in the store more than about 45 seconds longer as a result of my action.
I don’t pretend to hold myself out as the embodiment of courtesy.  I’ve been known to be assertive, and even rude at times, much to my chagrin.  We all need continuing education in basic courtesy, and some of us need the basics taught to us for the first time.  Sadly, it seems there’s nothing common anymore about common courtesy.