"I'm a war of head versus heart
And it's always this way
My head is weak, my heart always speaks
Before I know what it will say"... Crooked Teeth - Death Cab For Cutie
I am going to propose that the heart rules the head in the majority of matters.
I will explain it through this criteria: When people hurt us or challenge our ways, we feel it before we respond to it. All of life's complications that arrive through a sensory means, ie; through touch, speech, etc involve our heart feeling an emotion that needs to be translated in order for our brain to understand it.
This can be looked at in an example like when you get a "bad feeling" from someone you are likely to try to figure them out or reason why they behave in a manner you find to be objectionable. Some folks respond to a person immediately by how they feel about them. Others may decide to "give them a chance" based on criteria they personally set about them. Both usually result in the same diagnosis, however, the one where the heart or the "gut" decides immediately, may be the one closer to truth. This is judged with a factor like time being in the equation. In other words, when we find out "over time" what our instincts told us immediately we realise that indeed, our hearts rule our heads.
In another example, like say the breakdown of a relationship, our hearts or "gut" may well tell us in advance where we know the relationship is destined without rationalising it further. however, when we consult a factor like "memory" of the person or a snapshot of happier times, it may delay what we feel is the overall best solution to our dilemma. We often let emotions like Empathy override our initial instinct and the combination of this empathy coupled with our thoughts, the translation of the empathy passed from our partner to us and into "memories" through a thought process may also override our best interests in favour of a lost cause which we may already know to be true. This, in my opinion is again the heart ruling the head.
When the head rules the heart, often-times we see this to be as an experience.... a number of stimuli that amount to a situation being ruled by probabilities. Let's say for example you a find yourself repeating a similar experience from the past where a certain experience led you into an uncomfortable situation. Factors like the probability that another will manipulate you the same way as someone did previously or a recognised pattern of behaviour will lead you into a set of similar circumstances that were undesirable sets the probability that what you are experiencing is probably worth avoiding. This is typically a situation where the head rules the heart.
Another is more simply put. You may know a person to be unreliable in meeting your expectations which are again, an emotional response, not a logical one. You may really feel that you want them to come through for you, but then, through experience, you know it is unlikely to come to pass because you maybe asked this person to do something say like, 10 times but they have maybe only did it twice. This puts their probability at 2/10 which means they are unlikely to provide the assistance you need. This is another area whereby the head rules the heart.
As we are all sentient human beings, all of our experiences must meet our emotional needs before our logical needs. Simply put, we must experience a situation before we have any knowledge of it. This will maybe appeal to you if, say, you look at how you behaved when you were 18 and cringe. This is so because you have a stable base to work from. It is unlikely that you are anything like the person you were then because you have felt some kind of emotion that has steered your person to experience life differently. You may approach a situation similar to when you were young, but with the knowledge to back it up. You may not feel as embarrassed or as anxious in a repeated situation because your heart has processed it into logic and your logic used in order to deduce the same situation into probability. in other words, a situation you once experienced emotionally in all it's detail may have less of an impact on your person because you have learned or experienced it fully.
I do think however, that because we are older does not mean we cannot genuinely feel emotions like love, sadness, happiness etc like when we had no knowledge of their adverse effects as opposed to just their positive effects. Our standards change and we continually try to predict how a situation will unravel. It's fair to say a lot of similar people with similar characteristics may indeed behave and direct situations into the same way as we have once experienced, but it is unfair to say that everyone is predictable and exactly the same down to the core. For this my only advice would be to stop living in your head and trust your heart a little more. An experienced heart will never steer you into an undesirable situation once you have complete trust in it. After all, the only person who's going to understand exactly what your heart wants is you. If you spend too much time in your head however, you may find yourself experiencing some of those positive emotions ever again based purely on a handful of bad experiences. After all, aren't there so many different people out there? And if you find yourself biased and bored, put yourself into the company of those you consider "different" and keep experiencing something different instead of judging each situation the same way.