Given its popularity, do you really think Twitter is going to exit for less than $10B? Those exits are rare, but so is the position that Twitter is in.
I don't know what the odds are, but surely there's at least a 25% chance that twitter will fizzle out. So it's 25% chance of nothing, and 75% chance of, say, a 3x exit. I dunno, that seems crazy risky to me.
Someone commented below about the secondary market - that actually makes a lot of sense I think. I guess when you're investing in twitter there's enough liquidity in the secondary market that you can probably get out if you need to.
If these are the odds, the expected outcome would be that you more then double your money. 25%0+75%3=2.25
So 25% chance of nothing is almost certainly wrong.
Twitter can just as easily be great for it's stakeholders and fizzle out as a service.
Do you think ICQ is worth $10B?
Facebook is hugely profitable, but its messages are private...
And calling Facebook "hugely profitable" is a stretch.
Since "making something people want" is generally considered a harder problem than monetizing that service when you have something people want, it's not entirely irrational to focus on the former before the latter, even if it doesn't always pan out.