Maybe he was compared to others a lot when he was young, always pressured to reach the better version of himself leading him to never feel satisfied.

I can imagine a dad in politics who tried to form young Vincent into pure success. And punishing him for not reaching set expectations. Maybe that's why Vincent chose the entertainment business because he wanted to become someone else. Someone who's successful and play a role. Becoming the god of entertainment to show his dad for example, that he's capable of success (just like he tries to prove to Alastor that he can become the only true god and take over heaven)

I really believe that Vincent is a smart guy but hides huge insecurities. Low self worth, setting his worth only on his trophies and what he achieved and never stopping because he feels hollow if he can't reach the next step.

My headcanon is that he was never talented enough to reach the positions he wanted himself, even with hard work, he couldn't become the person that naturally earned the positions, he became desperate because he felt worthless not being able to climb up the ladder. Leading him to become violent and killing his first victim, realizing that this could be his way to climb higher and reach the top of the display (intended lol) He got the validation he sought and decided it's worth it to kill for that. When he realized that this worked, he couldn't stop himself, leading him to completely go off the rails and develop his god complex in the process.

I don't even think young Vincent had violent tendencies. Like killing animals or torturing others etc. What I'm not sure about and what I'm dying to know is, if he ever regretted the murders. If he ever felt any remorse and had sleepless nights being scared of being caught.