Good decisions require a mix of dispassionate, rational analysis and emotion.
Though we often hear of emotion and passion clouding the decision making process, research shows that feelings help us make better decisions. Specifically, emotions aid decisiveness. Humans who have suffered damage to the part of their brain responsible for emotions are prone to crippling indecisiveness.
Here's a metaphor I came up with that conveys the mix: reason is the steering wheel, emotion is the gas and brake pedal.
When you get in a car, you first need to decide where to go. You need to think clearly and objectively about the best route. Once you've decided on a route, you need to press the gas pedal at different intervals to move forward, to go faster, or to slow down and come to a stop.
Suppose you brainstorm a new business idea. You want to think about the idea clearly and assess honestly the pros and cons, market size, competitive landscape, etc. You don't necessarily want your emotional side to dominate this assessment process. Once you've decided you want to pursue an idea, dreams of success and emotional excitement enable you to press the gas pedal and put in 12 hour days.
If the business is headed for the gutter, and you need to take immediate action to right the ship, emotions such as fear of failure and embarrassment will accelerate the actions prescribed by a rational cost-benefit analysis.
I frequently have to remind myself that good decisions can have bad outcomes. Also, I'm still unsure of the role of intuition in good decision making, but I agree with Auren that it's better to trust your gut when it tells you not to do something.