Locus of Control

I had a conversation with someone today that made me think back to my Organizational Behavior class in college. I didn't really enjoy that particular class, but there was one concept that really stuck with me: Locus of Control.

This is from the Wikipedia article on Locus of Control:
Locus of control is a concept initially used to distinguish between two types of situations – those in which outcomes are determined by skill in contrast to settings where chance is the main determinant of success and failure. For example, in games such as chess, sporting events such as tennis, and exams in fields such as math, it is reasoned that positive and negative outcomes are determined primarily by ability and level of skill. This does not imply that chance has no influence whatsoever on what has transpired. After all, perhaps the tennis match was affected by a gust of wind blowing the ball, or the math exam score influenced by a guess at a true/false alternative. Nonetheless, outcomes in these events primarily are determined (or, are perceived as determined) by ability. Ability is located within the person; hence, the so-called locus of control is internal. On the other hand, if a “head” or a “tail” will be showing in a coin toss, or whether red or black will be the place the ball stops in roulette, is determined (or, is perceived to be determined) by chance (assuming the game is “fair”). Of course, some may think they can sway where the roulette ball stops or that they can guide the appearance of a head or a tail on a coin toss, so that ability may be conceived as influencing task outcome. Nonetheless, most individuals on most occasions believe that success and failure at these tasks are chance-determined. Chance is regarded as external to the person, resulting in the external locus of control label.

This term has also been used to describe people's personality. Based on whether one perceives his or her fate being driven by inside or outside factors. Again, from Wikipedia:

Internals tend to attribute outcomes of events to their own control. Externals attribute outcomes of events to external circumstances. For example, college students with a strong internal locus of control may believe that their grades were achieved through their own abilities and efforts, whereas those with a strong external locus of control may believe that their grades are the result of good or bad luck, or to a professor who designs bad tests or grades capriciously; hence, they are less likely to expect that their own efforts will result in success and are therefore less likely to work hard for high grades.....This has obvious implications for differences between internals and externals in terms of their achievement motivation, suggesting that internal locus is linked with higher levels of N-ach. Due to their locating control outside themselves, externals tend to feel they have less control over their fate. People with an external locus of control tend to be more stressed and prone to clinical depression.

I find that this personality trait is one of the first things I take notice of in my interactions with others. I listen to the things that they say, and how they perceive the world around them and the events in their lives. My experience has pretty much supported the above observation - that Internals tend to be more motivated and acheive more, while Externals tend to be victims and either flirt with or fully enter severe depressions.

I wonder what it is that causes the difference in perception for Internals and Externals.