That´s the power of Fantasy sports, and also why it is increasingly winning more and more players over the years. After all, not everybody can be a professional player...
As you mentioned, when we join a Fantasy competition we suddenly see ourselves cheering for players on your rival team and even for players that were completely unknown... Just because we want to get the most possible points and they are the key elements of our team. We really feel like a manager (with less stress I would say).
That is the best part. I have no stress over it. My favourite part of fantasy is the trading and trying new players. Never thought I would cheer for a Chief but when you have Tyreek Hill on your team you can't help it.