Why Rito Really Doesn't Want Sandbox Mode
Because if you can practice the same thing over and over again without restrictions you'll be too good at it and that won't be good for the casuals who don't have the hours to practice. Imagine spending literally hours a day practicing the same moves over and over, becoming insanely good at it. It's just like sports players who practice a shot or a dribble with a ball thousands of times.
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If you have the time to practice repeatedly, every day, you'll be better at it than anyone else. "Practice makes perfect." Ever heard that line? If there are people out there with time to do this, they'll basically be perfect, almost like those perfect bots from Perfect Dark on the N64 that always got headshots on you.
Casuals won't be able to compete against perfection. That's why Rito doesn't want it.