After start some topics about Shegorath and Cicero i organized information and probaly discovered the reason why Cicero becamed mad:
"The rest of Cicero's Family members die, and the laughing in his head has drove him mad"
""silence" in his head that is driving him mad and how he is welcoming it.
" In the final entry of Volume One, Cicero talks of a contract he had where he posed as an adoring fan of the Arena Grand Champion in order to kill him."
Source: http://elderscrolls.wikia.com/wiki/Cicero
By the information,even being confuse,and by the "case that the contract of killing the grand champion is an easter egg".Maybe true but...as we know he probaly "killed" or tried to kill the Grand champion(probaly the Hero of Kvatch).The information of trowing him to the waterfall and the bears it's possible the easter egg refernce.But this doesn't mean that the information can't be true.By his journals we can note that he is around for a long time,around the time of the Obvilion invasion.
My theory is that Cicero tried to kill the Grand Champion because of the contract,but failed and then runned.But the champion didn't searched him for revenge,because he is a good guy.But after the Shivering Isle he literraly becamed Shegorath.So all the felling,thinkings and pleasures was transfered into him.And we know how a Deadric Prince lives?Right?So the new Shegorath could have probaly using his mad power to drive Cicero to madness,becoming what he is know today(we know that Cicero was an smart man by his journals) and making him failing in his efforts to restore the Dark Brotherhood.
So what do you guys think?That i'm right?Or that i'm incredible wrong?

Wrong probably.
I dont think it was the CoC he killed, the dates in his notebooks dont match.

Also, I dont think the CoC becoming Sheogorath should be viewed as canon.
It is far more likely that the CoC only stopped the Oblivion crisis and that all the other things were done by other people.
The portal to the Shivering Isles was open to anyone and it was probably some other person that went through and became the mad god.
I know I have never played a single game of Oblivion where I became head of every guild.
He did not become Archmage or Gray Fox, those were probably other people. Otherwise it gets a bit ridiculous.

Cicero was driven insane because despite his tremendous loyalty, the Night Mother would not speak to him, and he was forced to see his beloved guild be reduced to ruin.
In a sense all madness is Sheogorath, so you have a point there.

Also does people like solitary Fisherman's and poor's that live alone, or isolated,or a rich(like Cicero) that thinked that had a great path to follow,was literaly destroied by it's belives and actions can be influenced by Shegorath too?

He didn't kill the CoC, it would've been a different grand champion

In the sense that madness and Sheogorath are the same thing, yes.
But (likely) not due to personal actions taken by the Daedra.
Think of it like royalty. The queen does not come into your home and starts laying down the law.
She sits in her palace in the capital city, but all the while in the entire land governing is going on.
Doesnt mean they have to be present personally.

cicero is this way, because he's living with a dead person, that he has to take care off + many of his old guildfriends got killed.

isn't this reason enough? i mean, i would go insane, if i had to clean a dead body for years

I have to agree with Merari I don't think the COC becoming Sheogorath should be viewed as 100% canon.

Mage's Guild splits and becomes two different colleges, only way I could see that happening is if someone else and not the COC became Archmage.

Technically Cicero goes insane because of the situation with the Night Mother and he wears the Jester outfit because that's the last contract person he killed and for some weird reason Cicero liked the person he killed.

Don't know if COC=Sheogorath is canon or not, but COC=arena champion is only one of the multiple posible options Oblivion gives you. That obviously is not canon and there has been many champions anyway. Then COC graciously letting him alive only to make him mad some time later makes not sense.

Remember. Cicero is an Imperial, and it's unlikely CoC/Sheogorath would've remained in tamriel and remained grand champion for a full 200 years, especially since the odds of the CoC being an elf are low

The CoC becoming Sheogorath is part of the lore now. Even Sheo himself tells you he was there when Martin turned into a dragon.

Lmao Wtf?

*Leaves quicker than he entered.*

That annoying fact annoys me. I can't accept myself being sheogorath himself. I wasn't even an Imperial!! I'm nord since ever. I can't look at myself and see a different "myself" or whatever.

Since you can CHOSE your race and so on in Oblivion, doesn't make sense to see sheogorath as yourself in oblivion. If you were a Orc... How did you became a .. Imperial?

I'm a nord since Oblivion. WHY.. tell me WHY..

somebody mentioned in another thread that TES universe operates under the philosophy of "if it looks, talks, and acts like a duck, it's a duck". In a similar way regardless of what the CoC was, once he became the Daedric Lord Sheogorath he began to assume the mantle of Sheogorath which meant not only his personality, quirks, and responsibilities, but also his appearance. TES is also big on destiny so it could also be hypothesized that the CoC refused to accept the mantle in full which caused fate to alter his appearance and mannerism in order to force the mantle upon him.

Daedric Princes can choose whatever form they want. For example, Hermaeus Mora appears as tentacles.

Yes,An example is Akatosh and Alduin,they are not dragons.We can imagine them as a "presence".Shegorath could choses the of a giant Chuck norris with 4 legs, 4 arms, 3 tails, and with a black skin, with vampire teeths and a witch Nose.They choose a dragon form only in the mortal world

The Elder Scrolls universe is... really... Much .. much more DEEP than I think it is. The more I learn the more I understand this.

That really makes me think: The man(s) who created all the T.E.S story are "Gods". They created an Entire Universe! That's scary, you know. I couldn't do it all alone.

Maybe I'm saying some cowpoops (Bull s*hits)

This is why i think games are better over movies.

Of course. Immersion, friend. It's all about what you ARE in the games. You drive the story... You tell the tale. You manage the time spent on anything you do. That's good..

Loose-Rock...

Hole in your logic: My arena grand champion was the listener. So, Cicero would not kill him.

That's my point. My CoC was also the Listener. There's no point in Cicero killing him. And no point in beeing sheogorath if I'm the listener. Oh well.

That.On another topic i said we shouled be abled to transfer the save of Obvilino to skyrim.This is what i said: "Actually would make more sense if we could import the obvilion save to skyrim.There are tons of edings at obvilion depending on your choice.At obvilion,if we completed the main quest before going to Sivering isles,we should be unable to enter there.if we becamed the grand champion we if we killed him,that should change everithing in the DA:B questline in obvilion.If we entered the Shivering Isles at Obvilion before the main quest,we would still be able to complete the Main plot,but we would be unable to keep playing.

But, my character was also Sheogorath. Plus, in Cicero's journals he says that there is another listener. I forget the name.