In brief:
Watching porn destroyed our reward center in our brains, when we do something enjoyable that we like our brain produces dopamine through the process of doing this enjoyable thing, when we reach our maximum joy the brain produces Endorphin to feel the trance of that joy, and produces DeltaFosB to make a memory of that experience that you just had in order to repeat it again later.
When watching porn our brain produces a flood of dopamine which is too much, that the brain has to gain balance so it shuts down your dopamine receptors in your brain, which leads to the following disasters:
1- you stop tasting small enjoyable things in life (like fresh air, seeing a butterfly, socializing ...etc) because they produce low amount of dopamine which should make a normal person happy and enjoy it, but not for an addict to PMO
2- you will loose the motive to have normal sex which produces a much lower amount of dopamine from what is being produced by PMO, taking you to have an erectile dysfunction or other sexual problems even that you're young and healthy
3- having sex with a real person (even your wife) becomes very difficult, because of many reasons (the partner is smelly[even nice human smell] and porn screens are not, the partner needs mental effort to put him/her into sexual mood and the porn screens not, sex with the partner can last for 10 minutes while porn can last for hours, sex with partner maximum once a day or every couple of days, but porn as much as you and only you want --> leading to not liking the normal sexual activities and always going to PMO
4- You will loose all motive to be a successful person in this life, because our unconscious mind keeps pushing us to be successful in order to be able to get a sex partner in order to move your genes to others, but when we see hundreds of naked ladies in one session of PMO our brains concludes that you are already having sex and already moving your genes to others and cannot differentiate between screen ladies and real ones, so it doesn't push you any more to be successful, actually you loose all your motivation in success in this life (and this is what's happening to me actually)
The experience of the Fapstronauts says that after 90 days of staying away from PMO your brain is to reset back to its Factory Reset and you can start rewiring it away from that destructive addiction that we have