Two years ago, one of my players, Denis, was thinking about running a game. There was some light pressure from the group for him to give it a shot. He eventually settled on trying to run a Gamma World game, details here and here.
That game never got off the ground. For Denis, he felt that there was too much pressure to compare to others in the group who have years or even decades of experience running games.
At the English camp we were teaching at through most of August, several guys were asking Denis and I about our games (some are former players, some just curious about RPGs). Denis mentioned that one of the main reasons why he never got his GW game going because the random encounter tables seemed overwhelming.
I instantly understood what he meant. Random tables like those in the books require the referee to be familiar with most of the creatures in the book. And with all the mutations in GW, that may make it overwhelming. If you only need to worry about a few monsters you've placed in a dungeon, plus whatever powers your players have for their characters, it's not as overwhelming. If everything in the book is on the table, it's a lot to deal with.
I told Denis that he should try to run the game, but just drop random encounters. The look of relief on his face was noticeable. I think he had been in the mindset that the game has rules for this, so he needed to use them. But that's not true.
You don't need to use all the rules to run a fun game. Especially when you're just starting out. I ignored lots of rules when I was just starting out as DM nearly 40 years ago. And the games were fun, and challenging. Once you are comfortable with the basics of the game, and with planning and presenting adventures, the more complex stuff can be added back in.