When people delve into philosophy for the first time, their initial guides are intuition and feelings. Because one does not instantly know the parameters and bounds of all philosophical thought, they rely on heuristics to guide themselves when becoming familiar with content. Due to their nature, intuition and feelings are often the most common heuristics. When we encounter a conclusion that seems wrong, it can be easy to dismiss it without further thought. Heuristics are important as time-saving mechanisms. However, they are not a substitute for proper philosophical thought. There must be a time when the training wheels come off. The cost of truth is relinquishing the comfort of feeling.
Most people have feelings and have a sense of intuition. Possessing either isn't necessarily a bad thing. However, elevating them onto a pedestal right next to reason is a grave mistake. Reason, when utilized properly is infallible. Since it is the method by which we evaluate truths about underlying reality, any resulting falsehoods must be the result of mistakes. These mistakes are often induced by our heuristics.
Feelings are fickle. They can change on a whim. You may feel one thing at a particular time and then feel something else the very next second. In their defense, they are usually representative of something about reality. It is peculiar to feel sad when there isn't something sad to feel about. It would be odd to feel angry about something when there isn't something to be angry about. Yet, we know that our feelings aren't reliable. I'd be shocked to meet anyone who never had one instance of realizing that their feelings at a particular moment were not overblown in proportion to the situation they were facing. Relying on your feelings to generate a worldview would create one full of error and prone to change as frequently as changes in one's mood.
Many do not view intuition the same way. Intuition is generally viewed in a much more positive light than mere feeling. This isn't without good reason, as our intuition can be helpful at times (as are feelings on occasion). Some groups even consider intuition to be more reliable than reason, as the Transcendentalists did. Unfortunately, this error can be far harder to spot than the previous one. We may reject truths that appear unintuitive to us in favor of falsehoods that appeal to our preconceptions. There are very few conditional truths, and questioning ourselves from time to time is the best way to avoid this error.
As some would have guessed, I present reason as the alternative to other ways of coming to a set of beliefs. What really prevents reason from being prone to error in the same way as the other two? People certainly can reason incorrectly and come to a false conclusion. This is true, but stems from an error on the part of the subject and not on the method. Perhaps that might be true for feelings and intuition, too, as you could selectively apply them properly, but it would be a mistake to see them as infallible in themselves. They do not possess the same universal form as reason does.
Reason is the ability to come to valid conclusions based on the use of logic. Reason prevents belief in irrational or unjustifiable assumptions. We cannot understand truth without reason. If we allow ourselves to believe in logical contradictions, we put the concept of truth at risk. Reason is important for evaluating one's actions. Our beliefs govern our conduct in the world, and it is instrumentally better to have our actions based on true beliefs rather than false beliefs. If you'd like to believe in the truth, be prepared to "pay the price". I am glad to say that I see many Deists do so already.