3 Answers

It is a cynical commentary on how life goes. No matter how nice you try to be to people, you will still be criticized and unappreciated. I don't happen to agree with the saying but I know that some do see life that way. Too bad for them.

I don't understand this quote. I never have. The times when I have done a good deed, I'm usually rewarded. It might just be feeling good about myself .... but there is a reward. (I just answered this.) Oh well ....

No Good Deed Goes Unpunished. 
Like Ducky said, one can do EXACTLY what is right and good, EXACTLY what is needed and/or expected, and SOMEONE will find fault with it.
For example: You weed your Mom's flower beds.  You have done a good deed.  She gets upset and hollers at you because what YOU thought was a WEED was a seedling of her favorite flower. 

Ducky

Oops!