Why did Quora's Charlie Cheever suddenly bow out of his day-to-day obligations at the question-and-answer site he co-founded in 2009?

Well, you'll only find a partial answer on Quora so far.

Aside from rampant speculation from Quora users, the only "official" statement regarding Cheever's unexpected exit came on Tuesday from co-founder Adam D'Angelo:

We decided it was best for Charlie to step away from his day-to-day role at the company. He will always be a founder of Quora and will be an advisor to the company. 

I have a lot of respect for Charlie and we wouldn’t be where we are today without him. Many of his contributions will remain as core parts of the company’s history and culture.

Charlie and I both continue to care deeply about the employees of Quora, the writers and readers of Quora, and want to do what’s best to see Quora continue to grow into a successful company that helps everyone share knowledge.

Both D'Angelo and Cheever were early, significant employees of Facebook before leaving social network to start the Q&A site. The pair together made Inc.'s 30 Under 30 list in 2011.

Cheever is a Harvard graduate who at Facebook worked on developing Facebook Connect and Facebook Platform. Previously, he was an engineer at Amazon.

Recently, Quora announced an expansion and move to Mountain View, as well as a closing of a $50 million funding round led by investor Peter Thiel. The Q&A site has also grown from 70,000 to 250,000 users in the last year alone, Forbes reports.