Coming from a GamesTM feature with Shigeru Miyamoto and Takashi Tezuka...
On designing the challenge and difficulty of Mario games:
“For me one of the things was maybe the gap between the really advanced players and the first-time players. The difficulty balance is always something that I hear frustrations about from the public, whichever way we decide to go. We always have the testing team test our game, but whatever they say is really fun, the first-time players might consider to be very difficult. One of the things I do sometimes at the later phases of development is go in and hear the testing team’s requests and actually pull that away and lower the barrier or change what it is they want. Sometimes I even hear from the testing team, ‘You’re destroying the fun’, but on the other hand, the flipside is you hear the first-time players saying ‘If I can’t clear a level it’s not fun for me. If I can’t complete a game it’s not fun for me’. The more years that have passed, the gap between advanced and first-time players has become wider.” - Miyamoto
“Even though we put a lot of time and effort into trying to balance the difficulty, when we actually release there are a good group of people who can’t complete the whole game, and so we always have that internal struggle of the gap between the advanced and first-time players. That’s why one of the things we’re trying with Yoshi’s Woolly World is to have two different versions of events for the advanced and the beginner players. We changed the performance of it, but then even in the beginner mode we did put a lot of stuff in there so that advanced players can still have fun. We put a lot of time and effort into trying to balance that out.” - Tezuka