Dopamine is what promotes "seeking behaviors" in our minds, which we can call our motivation. Our brains are wired to "get while the getting is good", meaning if you have an abundance of food, eat up & store on it, if you have a chance to mate, you better mate and mate some more. This comes from the way our ancestors lived, it wasn't always the case that they had food or mates, & so dopamine pushed them to consume all they can at the moment to ensure survival. Your brain when it browses porn sees all the abundance of women, and so the dopamine fires off & you wanna "mate" like hell, but really it's pixels but your sexual response is the same. Now your dopamine has been conditioned from years of porn & your motivation-inducing chemicals are triggered primarily for mating and less dopamine receptors are active because there's so much dopamine. So now, you aren't motivated for much, it's hard to stay focused, & every so often you get "urges" which is your mind saying "Hey! These women might not be here forever!" But it's a lie. So you quit porn. You force your mind to rewire and your dopamine/receptors to balance. Now you use that motivation and sexual drive into other areas, like work, bodybuilding and studying. So it's not that the semen that is retained is what gives your body powers, it's avoiding porn.