There are two definitions of ‘game designer’. They are ‘creator’ and ‘developer’ or maybe ‘inventor’ and ‘refiner’. These are both important jobs and you don't usually find them both in the same person.
‘Refiners’ need their adult brains turned on. They need to be critical, ask questions, test, and fix broken games. As such, people who tend to live in their adult mode all the time make better refiners.
‘Inventors’ need their adult brains to shut up. When you’re making something new, everything needs to be awesome. You need to stop second-guessing every spark before you manage to light the fire. You need to stop fixing the leaks before the ship is built. So people who can think with their child brains make better Inventors.
I’d say the biggest obstacle to your becoming a well-rounded game designer is your natural tendency to spend all your waking life thinking with your adult brain.
James Ernest, Reddit AMA comment