I thought that some of our readers might find useful, the following:
Looking at pornography and engaging your mind in sexual fantasies is a mental rehearsal of, among other things:For more, read: The Meandering Monk
— self-centeredness;
— selfishness towards others;
— using others as servants of your own pleasure and preferences.
Masturbation rewards that mental rehearsal with physical pleasure.
Thus, masturbation is a sin that trains you to sin more and more— not only in actions but also in attitudes.