It is a trite sentiment that annoys some people, but it is true... and important to remember.
How many people have ever gotten upset or angry while roleplaying... enough to ruin your fun? Of those remaining, how many have ever been part of a roleplaying session that was derailed when someone got upset or angry? If you don't fall into either of those categories, I suspect you either haven't been roleplaying much or you have been very lucky.
Back in the late 1990s, I was heavily involved in Vampire LARPs. There was a good bit of out-0f-character politicking, backbiting, and stress for many of those with whom I played. I wasn't immune to it. It took me moving halfway across the country and having some other roleplaying experiences to really get some perspective on what I'd been involved with. Gaming had become a responsibility rather than a recreational activity. It was a social outlet, but I didn't actually like some of the people that I was socializing with (not a surprise with a huge group). Was I having fun? Sometimes. Was it an efficient producer of fun? Not really.
Since I moved away, I have changed the way I approach gaming. If I don't enjoy a game, I don't play in it. That seems like a no-brainer, but it is a rarer attitude than I think it ought to be...