A year or so ago I wanted to work on some of my GM skills that are emphasized in games different from what I was playing at the time. It coincided with interest in D&D 5e and so I started to run a 5E game. Then from various tricks and twists of life I ended up running a second 5e game.
Now you can run any game any way you want, but the goal of running 5e was to run D&D - something that felt like the D&D games of old - and not my normal type games. So I tried running D&D in what I thought was how D&D was supposed to be run, supported by the books, streams, and even advice sections in videos, reddit, and other blogs.
It's led to two games that I like running, but as the first game has gotten higher and higher in level while I liked the game prep has become harder and harder. The PCs are level 14, they have ridiculous abilities, and they can basically break the rules of how D&D is "supposed to be run." Random encounters? Not really a thing. Ambushed at night? Not really a thing. Big bad boss monsters? My choices are over kill by going like 10 CR over the level of the PCs, or deal with the fact that an adult red dragon could probably be solo'd by one of the players if given time to set up properly.
And then recently I realized what my problem was. While trying to run D&D the "D&D way" I forgot about my own strengths as a DM. The idea was not, and is not, to change how I GM, but to brush up on skills D&D emphasizes that other games I play don't. Skills like running monsters more tactically. Ultimately, the way I was trying to run D&D made me very focused on what the players could do. And that's...a mistake. I've always said it was a mistake, but in my own game I forgot about that.
RPGs, and D&D especially, can serve as a wonderful power fantasy. The PCs will get powerful. They should get to be powerful. They should get to have fun with it. And with the game designed to do that, eventually you hit the problem where the players can do too much - if you are worried about what they can do.
The trick is to focus on what they will do. Limit choices. Make them actually make choices. Do they push on and go to the big fight exhausted and depleted from other things? Or do they give this one up? If two allies are in danger at the same time, which do they go to save - or do they split the group and try to save both while being less prepared for each individually?
My strengths are built on running around Choice and Consequence. I wasn't doing that. I was just laying out paths to monsters and encounters. So now we see how it works when I keep in mind that there is more to D&D than just that. Hopefully it works out well. If nothing else, I'm having more fun and less stress with the game than I've had in months.