"Outsiders always look for a reason to explain why they are not inside. They never look in the mirror. Let's face it, the profession I'm in is a very simple and a very cruel one. There is no way that you can create a career for someone without talent and no way to stop a career of someone with talent." - Isaac Stern, violinist
Stern was sometimes accused of getting in the way of artists he didn't like. This was part of his response to that criticism. I think it's very likely that people can and do suppress careers for whatever reasons they may have - professional jealousy, vengeance, financial gain, personal differences.... It happened to Mozart and Zelenka, just to name two. The irony (sometimes) is that those artists who are "black-listed" can (with time) come back and surpass those who tried to stand in the way. If Stern was ever one of those who actually dampened someone's career, he won't suffer for it - he was too great an artist.