There are two basic ways that we, as human beings, make decisions: logic and emotion. It's been said that men are more logical in their decision making and women are more emotional, leading to the traditional idea of why men and women just don't understand each other. This difference is hysterically illustrated in a scene from the movie White Men Can't Jump in which Billy (Woody Harrelson) and Gloria (Rosie Perez) are lying in bed. Gloria mentions that she's thirsty and so Billy gets up and returns with a glass of water. Her response:
...if I'm thirsty, I don't want a glass of water. I want you to sympathize. I want you to say, "Gloria, I too know what it feels like to be thirsty; I too have had a dry mouth." I want you to connect with me through sharing and understanding the concept of dry mouthedness.
Despite the silliness, this does illustrate the difference between logical and emotional decisions. Billy saw a problem and reasoned out a solution; Gloria didn't want her problem solved, she wanted someone to understand. In real life, both men and women make decisions based on logic and emotion, though to differing extents. Still, the relationship between these two modes of decision making remains decidedly one-sided.
Between logic and emotion, emotion wins very time. I'm not telling you anything new, this is the precise reason that salespeople act the way they do. They know that if they can create an emotional reaction from you, they have a better chance of making the sale. Why? Because emotion trumps logic. In fact, when you make a decision based on emotion you'll often find yourself rationalizing that decision later...you actually twist your own logic so that it goes along with the emotional decision.
You can never reason with emotion, no matter how hard you try. You can logically know something is a bad decision and yet still make it because your emotions are in control. We typically say that women fall victim to this when men do the exact same thing, just in different circumstances. He really didn't buy that sports car that gets 15 miles per gallon because it was a logical way to spend his money.
So your emotions can affect your logic and logic has no ability to retaliate. What can you do? The thing I've tried to do is determine when each is appropriate to use, which can be summed up in a simple phrase: in matters of the heart, listen to your heart; in matters of the mind, listen to the mind. This basically means that if you're trying to figure out calculus, you use your logic and problem-solving abilities (no amount of feeling is going to help you) and if you are attracted to someone, trust your heart and go for it (because no amount of self-talk is going to convince yourself that you're not attracted to him/her). I actually think the latter case is more difficult since we tend to run through romantic scenarios in our minds frequently, coming up with reasons why it won't work...the emotions scare us, so we try to logic them away. You could get hurt! Run! Yet it doesn't really make you feel better to stay away, in fact, it makes you feel worse.
The decision-making process is incredibly complex. The most important thing to remember is that emotions always win, so if you can keep them out of decisions that should be logic-based, you'll be better for it. This is precisely the "killer instinct" that is often cited for athletes, those who can shake off a bad mistake and still perform at a high level. On the other hand, don't try to logic away your emotions when your emotions should be making the decision...it doesn't work and it's not worth it.