Ben Fowlkes has an excellent piece detailing the oft-discussed 'Octagon Jitters'

There's a name for this phenomenon: "Octagon jitters." It's when the pressure of performing on the biggest stage in MMA causes a fighter to freeze up. It's been known to turn black belts into white belts and make world-class kickboxers leave their chins wide open. It's why the odds are often against fighters making their UFC debuts, and why many of them find themselves wondering what happened once it's all over.

Fowlkes goes on to describe the details surrounding Kenny Florian's fight with Diego Sanchez and Rashad Evans fight with Sam Hoger.

There are two points that I would like to expand upon for Fowlkes initial premise.

I feel that there are types of "Octagon jitters." For instance there is a serious difference between debuting in the UFC and being a TUF alum with all the added pressure and expectation. Fowlkes even makes this point, though not explicitly, when he details Shane Carwin's successful debut compared to TUF alums Kenny Florian and Rashad Evans. Jon Jones is another good example. Though you can just as easily lose your UFC debut a la Ryan Madigan.

Then there is something that I would like to call "Pride-octo-jitters." This deals with fighters who are making the transition from an organization that has different rules and venues, a fact that is often overlooked. Whether it be elbows in closed guard, lack of foot stomps or knees to a downed opponent or just a cage versus a ring; all can have a serious effect on a fighter.

The Octagon itself is a strange beast for a fighter that has competed in rings most of his life. The cage gives advantages to wrestlers and can be a useful tool at neutralizing submission fighters. The Octagon's massive area also allows for fighters to be more illusive compared to a smaller cage or ring, where a fighter could be more easily cornered.

Some fighters handle the transition easier than others. For instance, Quinton 'Rampage' Jackson versus Mirko 'Cro Cop' Filipovic.