In the end, we are likely to be punished for our kindnesses.
As far as the movie is concerned, this is merely a bridge in the conversation between two characters. However hidden in there is a pithy summary of the effect that random acts of kindness (not selflessness) have.
This statement asserts that the most likley outcome for ourselves of any kindness on our part is a negative one. Should you find youself in a situation doing some act of kindness, the universe will notice (in as much as the universe notes anything) and it will return upon you some sort of retribution for having interfered with the natural order of things.
When one undertakes a kindness, one is irrationally placing someone else's needs above yours. Were you to rationally aid someone, it would necessarily be out of some perceived self-interest---acknowledged or not. Because of this, a kindness can only arise when a person is not afforded the time or opportunity to rationalize their response to a situation. If you have time to consider your actions and its implications, then you cannot be performing a kindness.
This isn't to say that one can't decide to do something against one's own interest, or that one can't rationally decide to do a good deed, all it means is that those sort of actions are not kindnesses--regardless of how negative the consequences may be for yourself. A kindness is that which is undertaken without consideration for its effect on the self. In this way, we find that those negative consequences destined be visited upon you easily arise.
If you choose to believe that randomly trusting or performing deeds without first giving it thought is more likely to end negatively than positively, then one can see how making an a-rational decision to lend aid to another is simply more likley to encounter a negative response. Personally I find that argument a bit too sterile. For me the more convincing (and perhaps simply a personification or extension of the first) argument is that there is a tendency in the universe toward balance. One cannot long have too much of one thing at the expense of another. To that end, there are bad things that happen in the world in direct proportion to the good things that happen in the world. When one embarkes unselfishly on a campaign to subvert the universe and aid another person, one is upsetting the balance of the universe. The easiest way for this imbalance to be corrected is for the universe to impart upon you some sort of retribution. That is the punishment for the kindness.
Those acts which are rational in nature are simply serving some self-interest. These rational self-interests may be natural, or supernatural. Available immediately or postponed to the afterlife. You may feel you will recieve, or at least deserve, accolades and recognition for some perceived act of selflessness, or you may expect some karmic reward in the afterlife for the same. Regardless, it is simply a delusion to believe that these potential benefits are not the core of much mutual aid in the world.
There are, however, countless examples of true kindnesses. As a particularly easy, yet extreme example, one simply needs to read the stories of those selfless individuals who have received the Congressional Medal of Honor--an award which can only be given for true kindnesses--and note that since WWII, only 37% of the CMOH recipients were alive to receive it. Some may say it's particularly cynical to believe that the universe punishes kindness, I don't think it's cynical, after all, the universe simply tries to maintain balance and doing so necessarily requires punishing acts of kindness.
One little corollary to this whole thing: while the universe may maintain balance--agressively at times, I do believe that there is no evil in the world save that which man does unto himself.