The mind speaks the language of our words.
The heart speaks the language of our soul.
Within us all they exist, and in general, smoothly trade a host of minimal decisions they face throughout their existence, in acts of diplomatic regulation to maintain each individual body which carries them. However, when those intense, history effecting choices arise - which neither are prepared to lay down their guard for, the relationship between the two becomes tumultuously hostile; and problems develop from basic issues, to all out battles.
The mind articulates words in attempting conversation with the heart. As it rationalizes excuses in justification of suppressing the hearts desires; "it will hurt the machine which carries us, leaving them open to all elements of pain, attack, or even capture." "It serves no purpose, we must close it off". "Don't worry heart, I will give you one of the major ones, eventually". The heart, however, communicates using an ethereal soul; therefore is unable to understand both the language of the brain, or its pragmatic sense of logic. All the heart hears is a mixed up jumble of bizarre tones, attempting to overrule its wishes; it knows its desires are pure and honest, but seems unable to enforce its point to any effect - no matter how hard it tries.
As these two dominant powerhouses create conflict over a battle for supremacy, the surrounding elements of the kingdom they fight within begin to erode, yield under the pressure of maintaining such a battle, and eventually - if no form of agreement is reached, collapse. Unfortunately, the carrier of these two organs has spent so long listening to and being taught power in the sights and sound of words; a clever action of the mind - they have come to both trust and rely upon their messages, they are no longer aware any other form of connection exists. They sense it, feel it, and are compelled to trust the silent screams of the heart, but more often than not choose in favour of the mind; the robotic computer system which overruled its initial creator. The mind wins and grows a little stronger, the heart loses, and the light glows a little dimmer.
The moral is simple; while it is often both useful and necessary to fight with yourself - and there really is no other battle in life but this one. When it comes to full-out internal war - everybody loses. And when it comes to intense desires of the pure variety; while the heart doesn't mind the mind, the mind really doesn't have much time for the heart - only a moment, here and there.