When talking about raid mechanics and expectations with new or inexperienced players you often times need to take a firm and authoritarian tone, when explaining what you can and can't do this can often times come across as condescending even if you don't intend it too. I used to run a very successful raiding guild in WoW and many new members often thought I was rude their first run. I admit I sometimes was a bit rough around the edges. However I whipped some of the most lack luster players into top tier raiders.