No good deed goes unpunished

[NeverendingR]

What does the saying "no good deed goes unpunished" mean exactly?

[Quizmonster]

This is a quote from Clare Boothe Luce, an American playwright and diplomat. She is known for her wit, which often involved saying things opposite to what had already been said or might be expected. Here's another: 'Communism is the opiate of the intellectuals', said to counterbalance the communist Karl Marx's idea that 'Religion is the opiate of the masses'.
What she meant by the 'good deed' one was probably the idea that helping someone often leads to his resenting you rather than feeling grateful.

[Quizmonster]

As further explanation, here is another possible situation that might apply. You may have given a local beggar some money on one occasion and now he expects you to repeat that every time he sees you. Thus, your original good deed now frequently returns to haunt or 'punish' you.

[Loosehead]

QM is as usual spot on, I just thought I'd furnish another example of this phenomenon. This happens all the time, one of your mates is a bit skint so you lend him a tenner for example, now you don't want to ask for it back but in the end you have to and suddenly you are made to feel like the bad guy or worse that mate will ignore you or avoid you if he can't afford to repay you.

[Catso]

This is one of my favourite sayings - the times it happens to me...

I take it to mean: if you do someone a favour, then events will conspire to make you a worse off than if you hadn't done the favour. NB, usually it isn't a deliberate act on the part of the receiver of the good deed.

A simple example: if you're in a queue of traffic running up to some lights, and you let someone out of a side road into the queue in front of you, the lights will change so that they get through and you are stopped.