Fun vs. a Good Run

[Li Shenron]

I don't fully understand the original question because for me playing or preparing/running the game seriously is the fun...

But at least I don't think "seriously" necessarily mean to plan everything and then manage to make the plan come true, or to fell overly responsible for everybody's fun like you are the only one in charge of that. It's not necessary for the DM to try be a God with everything planned beforehand, while the players play almost entirely at the table. The DM also can play at the table, doing the same things that players do (only not openly but behind the screen) including writing the story in real time, coming up with ideas and taking notes for the future about what the players (or dice) make happen.

I've never tried the following, but I would like one day to fake I have prepared a game, and instead come to the table with nothing except some random tables to roll on, and then let the plot emerge from player's initiative and dice, adding some ideas of my own in the real time... It might be quite extreme, but who knows maybe it won't be noticeably worse than when I try to prepare everything

 

[Mishihari Lord]

Li Shenron got it, the OP is presenting a false dichotomy. People find all kinds of things fun, even serious things like chess and reading classic literature.

Before you can get advice on balancing "fun" against "the serious stuff" you need to let us know what kind of fun you're talking about. Is it over-the-top combat? Cracking jokes and quoting Monty Python? Outrageous silly roleplay?

 

[Jhaelen]

People find all kinds of things fun, even serious things like chess and reading classic literature.

What's serious about chess? (case in point, I guess...)