Sometimes, when we meet someone we instantly like or dislike the person. Are we always right? Lets think about it! How many times were you actually right? How many times it was just a huge mistake? Maybe you met this person that really seems to be very nice and suddenly you realize that they aren't. Or you met the other person that you thought he/she was abominable, but it turns out that this person was helpful and a great friend. That feeling, which we usually call intuition, is just a result of our previous experiences. It is very important to listen to this feeling but we can't take this as an absolute truth. For example, in a job interview if the interviewer take his intuition as the only base to choose the right person, it would be an enormous mistake. But if the employer just use it as another criterion it would be very helpful.
Every relationship that we have experienced is in a safe place somewhere in our memory, even the small ones, and the ones that we think that weren't important at all. Our brain separate every information in categories, for example, if you meet someone who, in some way, did something that from your point of view isn't good, all his/her characteristics are considered a bad person's attributes. The same thing happens if the person do something that you think is good.
What we really need to be careful is with generalizations. Just because someone who hurt you has black hair doesn't mean that everyone who has black hair is going to hurt you too. It might looks like a very bad example but our brains really do silly things like that. Our brains just associate physical or mental aspects that they think are relevant but it doesn't mean that they really are.
When we meet someone and feel something bad or good about him/her, the most correct thing to do is to analyze which characteristics provoked this feeling. Then, we have to separate which attributes are relevant. After that we can rationalize it, and decide if our intuition has reasonable basis.
For sure our previous experiences are useful, that is the main reason why the human race still exists, we only need to be careful and use our powerful intuition wisely so we can avoid prejudgments.