I'll break it down real simple like.
Dopamine is the chemical that your brain releases when you achieve something that you percieve as achievement.
When you watch hardcore porn an jerk off your brain releases DOPAMINE in MASS AMOUNTS.
If you have only ever been an infrequent user of porn you might be able to get away with this.
BUT if you are a frequent/habitual user, you become DESENSETIZED to lower forms of Dopamine release.
What are these "lower forms"?
Having REAL sex (yes)
Hitting a PB at the gym
Getting a raise
Saving enough to put a deposit on a house
Going to a party
Basically, over time EVERYTHING in your life becomes less pleasurable. **** that should give you a buzz becomes BORING. This can lead to depression, laziness, social anxiety, being angry all the time, not giving a **** about anything etc etc etc
Obviously theres degrees of this but the more you use porn, the worse it gets. Porn is PROVEN to be highly addictive.
So the point of Nofap is shutting off this overstimulation and over time, (3 months tends to be a baseline to see reasonable results) your brain un****s itself so..... all that other stuff becomes interesting and desirable again.
So in short it's all about the DOPAMINE and resetting that **** to normal levels.
Footnote:
Before getting angry and saying this is all BS, think...I mean REALLY think if theres a CHANCE that any of the above applies to you, because if you DO have even a mild porn addiction, quitting that **** will up-level your game SIGNIFICANTLY.
I was a moderate porn addict who quit so any questions about my experience ask away.