this post is obviously in the context of professional illustration/visual arts, but it applies to hobbyist art spaces incredibly as well.
**especially cosplay**
generally when someone starts burning their bridges in the community, this is the attitude that fuels it, more than a lot of other issues
If you can't celebrate anyone else's achievements and treat everyone as your competition, don't be surprised if no one will stick their neck out for you and all you have left are enemies.