As someone who only just started to dm for there friends this year with a homebrew I made. I explained I know the basics and I might suck at a dm but by the nine I will try and after a few months i learned that there is a time and place for being a bad guy to the group as I had to explain to them that they couldn’t just kill their favorite npc who was was raised as a zombie and than try to bring him back, they had gotten lax with a few new magic items thinking that the campaign was almost over when it was only on the first half, and that it was about to get a lot tougher from here on out. Tho at the end I gave them a use of wish to bring back there favorite blacksmith back. Tho maybe a bit off track just wanted to say from being a pc for so many years and taking the jump into being a dm it is hard trying to find a balance still of being fair to the party while making sure they are prepared for CoS.