There are a few words, that some people find uncomfortable to use.
Those words are Thank you and I am sorry.
I wonder why some people have so hard saying those words? Take the word Thank you for example. Is that not an obvious thing to say when someone does something for you? Not all people would agree with that and I wonder why? Is it that if they would give another person credit for something, they feel that they are putting themselves down admitting that someone else is doing something good? The same as with giving a compliment for a well done job? Not everyone is capable of doing that! Or is there any other reason? It can't just be a matter of manners as I am sure we all are brought up to be polite etc.
The other words I thought of seem even harder to say - I am sorry! Admitting that you were wrong is for me a sign of strength but for some people rather a sign of weakness, I think.
In a relationship it is most important that both parts can admit their faults. How would it be if one of them in an argument always was the one that had to yield, just to put an end to the argument? The self confidence would surely suffer, thinking that he/she was always the one at fault.
We all do mistakes from time to time, and we all should be able to apologize. What brought this up then? Just something I saw on TV the other day and came to think of.
Thank you for reading and I am sorry if stepping on someone's toes now! 
Usksider
Pro 
If someone holds up a door for me, then it is nice, but I won't bother too much if they don't. But if someone hurts me and won't apologize, it will hurt me more. So this has a deeper meaning, I think.
At least, those I have got to know have very good manners! 
We're back to good manners again aren't we? Cost nothing, but mean a lot.