Upon thinking about karma, and the various related effects, one can quickly see that ones actions are not entirely independent of everyone else.  I have long thought that there must be something strange going on, because no matter how little I change my appearance, others notice it.  Sometimes this change in appearance goes on to affect others.  This in turn sometimes continues to affect even more people, whom I have had no contact with.  It is this affect that I now write about.
    One event appears, at the time to be entirely unrelated to anything else.  Many people in fact think that their behavior only affects themselves, and so they behave in manners which are disrespectful, because they do not in fact realize that they are indirectly affecting other peoples moods, and thoughts.  Imagine for a moment that a person is in a grumpy mood one day.  He gets up to the far too bright morning, and hurts his eyes when he opens them first, because his curtains are open.  He continues throughout the morning, burns his toast, spills some coffee, and is generally having a terrible day.  He gets in his, as he now notices, dirty car, and slams the door.  His neighbor upon hearing this, having been out early in the morning getting his/her paper, asks himself, 'geez, what did I do?'  This small change in mood can go one of three ways, the anger can infect this neighbor, the neighbor can be unaffected by the action, or the neighbor can become self-conscious and can distract him from other things.  The two polar conditions have effects, and so, just on random chance, we could assume that there would be a two thirds chance that the neighbor is affected in some way.  As one can see, already in the first minutes of the persons day, he could affect someone else, who could potentially affect someone else, and so on.  Now imagine that this person (the grumpy one), cuts people off in traffic, making them angry, and maybe his anger influences a deal at work, and by the end of the day, the person has just on pure chance, affected at least one other person.  As with the previous effects, the balloon effect would again occur, and so his mood that one day has now affected many people he did not have any intention of affecting, and possibly hurt people that he had no intention of hurting.  Now, I have to realize that this is only one person, in a world of over six billion people.  Given the number of moods (which vary according to who you talk to), probably about one hundred distinct categories of mood, at the level of at least aggitated, at least nervous, at least somewhat pleasant, etc.., that means that for any person, again assuming random chance, probably at least six million people per day are at at least the level of anger of our example.
    The previous example was only a mood, taking that out of the argument, we have simple actions.  So here is something a little more realistic, and something that we can see.  A person goes drinking and drives home.  On his way home, he kills a young mother, and himself, in a car accident.  The mother was a scientist, at a local national laboratory, working on medical research for a cure for cancer.  She did not document her work well, but had some very good results with several types of cancer, and many believed, in the field, that given a couple years, she would have produced a general cure for cancer.  The repercussions are very obvious, and so we see that this person, who only thought he was going out to have a good time, and probably was only concerned about driving for getting caught by the police, has delayed a cure that could have potentially affected millions of cancer patients.  This is only one possible outcome, of this event, and perhaps instead, the woman was pregnant with her first child, the child of  her husband, who died another car accident.  Therefore with one stroke, this man has annihilated an entire line of a family.  The possibilities are endless, but one never knows.
    I began with how connected things are, and gave examples which may have convinced you or not, there are further examples in my Karma example.  These are very simple examples, though they could get even more complex, and involve who someone could have become, instead of who they were, but I hope these were effective enough.  This topic has long been thought about, and is ultimately what many people have based religions upon.
    Basically though, the point is simple, ones actions never stop with oneself.  They will always affect others, this is not some mystical process, of your thoughts directly affecting the outcome of a situation, but instead one must think about it in the manner that that has merit because ones thoughts affect oneself.  If one thinks about a certain course of events, it could affect one's mood, just thinking about a bad outcome can darken one's mood.  The change in one's mood can affect one's behavior and one's behavior can affect others.  This line can go on forever, or it can stop, and I won't claim that every time someone does something, it will affect countless people, or even have the effect that one wants.  Should one be doing it for a purpose, though the interesting thing is that this line of thought does not rely on that.  What I have been saying is that sometimes, it will.  These times that it does, could balloon.  Further, over the course of one's life, the combined change of all of these could be significant.  Perhaps the best example I can think of is this.  Supposedly one day, Sir Isaac Newton was sitting in an apple orchard, thinking, as philosophers are want to do, and an apple fell on his head.  In a moment of inspiration, he thought about why it did that, and after some time, came up with a cogent theory of gravity.  I would ask another question in this example, though.  What made the apple fall, in a more original sense.  Did the bird that landed on the branch, knocking the apple out of the tree, or the wind, know that it would change the course of human civilization so rapidly?  Many things all have to happen in concordance, but some course of events started such that the end result was the falling of the apple, or perhaps this was just a single event on a line of events (someone startled the bird, the bird re-alighted on the branch, the falling apple gave Newton a bump on the noggin, he went to his wife to ensure that he was uninjured, his wife went into town, stopped to give a begger some money, which he used to buy a pen, with which he wrote about revolution, perhaps his name might even have been Roussou  -- total fiction, but...).
    Many people think about the desired results of their actions, but sometimes, one should try to think about the side-effects (effects that merely co-occur due to something done along the way, possibly unintentionally).  No one could possibly understand all of the side-effects of any event, but with practice, and with the knowledge of how one's actions affect others, one could use this knowledge to minimize or maximize the effects one seeks.