The mind is like an infestation of the soul
A new mind arises only when an old or previous one passes away in misery, that is if the volition of the mind at the stage of passing away was full of misery. Hence a new mind is born out of misery. And what is it born into? It is born into misery again! The miseries of birth, the miseries of life and finally that of death.
That is why the mind, that is the untrained and untamed mind likes to dwell in misery. Whenever it gets a flicker of a chance, it will and does pick up the negative from a neutral incident.
For example, imagine being in a quiet environment for some time and you are not aware of any celebrations about to take place. All of a sudden, you hear a very loud noise, which makes you jump in your seat. Chances are, that the untrained mind will naturally gravitate towards a more negative potential cause of the sound. And in that moment, it will embellish creating blown-out-of-proportion scenarios around that cause, which almost always results in some form of fear - another component of grief and misery.
And then you find out that firecrackers were being burned to celebrate the winning of some game. Even at this point, as you physically relax, the mind justifies the fear - "Well, it could have been something more sinister!" And what ensues is a conversation within different parts of the mind, that is different thoughts - one maybe telling the other "It was silly to be so scared! I know I'm in a safe place." And then another thought arises to rebuke the previous thought which justified the cause for concern - in the process, increasing the amount of mental agony or misery.
Hence the mind arises out of misery, indulges in creating scenarios of misery, survives by feeding in misery, thrives by projecting misery to other minds and finally passes away amidst all that misery to spawn another new mind. Unless this process of creating misery is broken at one point, the vicious cycle continues.
Now what happens when the mind is confronted with more than its capacity of misery that it can deal with?
Depending upon the current state of the individual mind that is dealing with the situation, one or several things can happen:
1. The mind shuts down from reacting
(a) Partial shutdown to the perceived source of misery
This is seen in unhappy married couples, who put their entire attention to their child as a means to get over the bitterness in their own relationship with each other. Only when the child goes away to study or work, their emotional intimacy returns.
(b) Complete shut down towards all reactions
This is used by the ego self to separate itself from another when it feels that wrong had been done to itself. It creates a distance from the feelings of the heart and thrives on justification of it. This is what creates relationship breakages.
Both (a) and (b) above can be short term or long term
2. It loses cognition and cognitive functions
This typically happens when the source of misery is one that is sudden and is seen as a great loss to the mind. This is typically for a shorter term and it recovers from that sense of loss gradually under normal circumstances or rapidly if it can get something to clutch on to.
Example: Loss of someone loved, which was totally unexpected. If there is no other distraction to counter that loss, it takes longer to heal. If there is someone, e.g. a little child that needs to be taken care of, the mind will use that relationship as a fall-back mechanism to counter that loss.
3. It reacts violently against the mind projected external source of misery as a means of disassociation.
This is similar to 1(b), but with a different reaction.
This happens when the mind perceives that it has been wronged, as triggered by the egoic self. This in turn, triggers the pain body, which then spawns anger. Anger is seen by the mind as a source of power to oppose the other and potentially 'right the wrong'.
4. Complete Breakdown
The final stage, when the mind is completely and utterly unable to comprehend, let alone deal with the misery, happens when the mind goes through a breakdown. This has several facets to it:
(a) When the person whom the mind inhabits is termed 'insane' as the mind is perceived to have lost sanity
(b) When the mind loses memory functions under the burden of misery - this is what is termed in medical terminology as dementia.