Just play well and don't be an asshole, and you'll get where you need to go.
If this seems simplistic, it's because it is. I don't entirely agree with him, and I'll get to that in a minute. But for now, it's a good starting point. If you've spent years in music schools and the professional world, you'll find that a lot of people disqualify themselves from advancement without even knowing by failing one of these conditions. Sometimes, though rarely, it's both. It's simple, I know. You don't need to be a youtube star. You don't need to hype everything you do to everyone within earshot. To be honest, as much as I hate to admit it, it's even possible to support yourself without presenting anything earth-shatteringly novel in your playing or teaching.
However, there are two sides to every coin. The flip side is this second maxim. I first heard it from a dear friend of mine at Princeton who studies physics and computer science, but I've found it applies just as well to music, and I'm convinced that it's close to a universal truth:
There is no correlation between being nice and being successful.
If there were, how would you explain the success of people like this guy?
I'm not saying to model your life after him, or even that his vices contribute positively to his art. Far from it. But I am saying to get over your fears, big or small. There is no 'Blacklist' out there that some studio executive, concertmaster, Russian mobster, or ghost of Dorothy DeLay is circulating to bar you from employment. You can be the biggest douchebag in your music school. You can denigrate women. You can get kicked out of every house party before you hear about it. No matter what people might think of you as a person, if you're doing what it takes to be successful, chances are you will be. Some of the worst people I've ever met I met at Juilliard, and most of them are now enjoying careers that you never will.
If you think that's unfair, then I don't know what to say, because sometimes life isn't fair, at least by your definition of 'fair'. Wherever you invest your time is where you will reap the rewards. If your orchestra manager hates you for ditching but you won the Tchaikovsky competition in the meantime, they can't take away your medal. It's nice to have a few good references when you graduate, but that doesn't mean that karma will fail you at life if you ditch a class. You can treat your girlfriend like garbage, and it could have happened on another planet for all your 86-year-old teacher cares.
For the record, some of the best people I've met in my life I've also met at Juilliard, and some of them are also enjoying stellar careers right now. I'm not saying being nice is detrimental to your career. It's just unrelated.
I don't know how to define fair. The world would be a terrible place if it were fair as I see it. But I am reminded of something Jesus of Nazareth said 2000 years ago:
He maketh his sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust.