My belief is very similar to the one given by James the Just; that we are born with natural, animalistic impulses. We are also given free will and have been given, by some avenue or another, instruction on what is right and what is wrong. It is up to us to use our free will and, as Bill_Lins put it, our self discipline, to overcome those instincts and do what we know is right.
In Freemasonry we often say that we give men tools to make themselves better. The fact of the matter is, every man already has the tools. Explaining to a man that he should be a good person by way of metaphors doesn't give him any more direction than just telling him he should be a good person. To me, the benefit of Freemasonry is putting into context WHY he should be a good person. I've heard it said that current generations don't know the difference between right and wrong. I call BS on that. They/we know, they/we just choose to ignore it. Let's be honest, the carnal pleasures of life are fun. I could spend the weekend knocking over a liquor store and using the money to buy hookers and blow and have a great time, so why don't I? Because I know it's wrong (and some other reasons, but it's an example, just go with it). So, what is the benefit of doing the right thing? Ready for the bombshell? Okay, here it is...in MY opinion...not a damn thing. There is absolutely no benefit (in terms of the big picture) to right action. HOWEVER, there is infinite benefit to becoming a good person, and becoming a good person has to do with diligently working to rid oneself of those base instincts that serve as motivation to do bad things. It is only through the constant application of self discipline that we can hope to ultimately transform ourselves. And I honestly believe it is the most difficult task that someone can ever undertake, but also the most important.
I work on it every day, and I fail everyday. Some days I do great, others, I mess up. But I keep working at it relentlessly and I can say for certain that I am better today than I was a year ago, and if I remain vigilant, I'll be better in a year than I am today. My goal is to someday be perfect. Impossible you say? Maybe, but I can guarantee that I'll fail if I don't try.
(For the brothers here, yes, I realize how similar all of this sounds. I could've written the whole thing with Masonic symbolism, but I refrained for non-Masons. If you are a Freemason and don't know what I mean, reread it, think about our symbols, particularly from the 3rd section of the 1st degree)