TLDR
Nothing to interesting, they got in relatively late and are now selling a part to give it back to investors while still keeping the majority of their shares, so this has nothing todo with them not trusting in Facebooks vision any longer.
1/ Return some capital to investors
2/ Start up a new fund to invest in other things?
They would've sold their entire stake if they didn't believe FB would grow anymore.
It wasn't a comment; it was a question.
What's silly is to respond with a fact-free retort that provides no value whatsoever to the discussion.
Although I'm no investing expert, it's my long-held understanding that investors don't hold onto stocks that they expect to go down, and investors don't sell stocks that are expected to rise.
Currently Facebook is generally recommended as a "buy" or a "strong buy", and price targets are around $60. It's possible that Andreessen's motivations had nothing to do with their expectations of the stock's performance (versus other stocks that they may have set their sites on) but I tend to doubt it.