Oh, you mean Pansy mode?
When I first played Halo, I would always do easy so I could have fun, but the enemies weren't much of a threat. It was alright, because I sucked at FPS games. At one point in Halo 3, I decided I actually wanted to be good at this game, so I made a point to always at least play on normal. And then I got used to that.
The first thing I did for Halo: Reach was solo it on Legendary. I have also done the same for Halo 4. The matchmade Firefights in Reach are also automatically Heroic, so I got used to that difficulty as being one of the norms. Now the de-facto Normal isn't much of a challenge at all.
Instead of Easy → Normal → Heroic → Legendary, the difficulty scale has become Pansy → Relaxed → Normal → Hard.
But not everyone is me, so I don't criticize the difficulty level they play.
Unless we happen to be playing co-op, in which case you better step up to at least Normal. Even if we're just running through to do an Easter egg, I refuse to play Pansy with assistance. We should be able to breeze through Normal just fine. If we're looking to fight side-by-side to overcome an actual threat, then it should be Heroic. If you want balls-to-the-wall tense action and uncertain outcomes for high rewards and Teh Achievements, then the situation should ask Legendary of us.
The same seems to hold true for (most) other games, I can adapt to and play Normal with little difficulty right off the bat. There are some supposedly tougher games I haven't tried though, but normal seems to be the rule of thumb for my casual play.