It all depends on what one decides to be a definition of a "success story." For some entrepreneurs, it might be getting acqui-hired, for some -- a $10M exit, for some -- a $200M exit, and for others -- an IPO.
Based on the numbers I have anecdotally heard in conversations over the last decade or so, VCs fund about 1 in 350 ventures they see, and of all of these funded ventures, only about 1 in 10 become really successful (i.e. have a big exit or a successful IPO.) So you are looking at a 1 in 3500 chance of eventual venture success among all of the companies that try to get VC funding. (To put this number in perspective, US VCs invest in about 3000-3500 companies every year.)
In addition, there might be a few others (say, maybe another 1-2 in every 10 companies that get VC investments) that get "decent" exits along the way, and hence could be categorized as somewhat successful depending on, again, how one chooses to define what qualifies as a "success story."
Finally, there might also be companies that may never need or get around to seeking VC funding.
One can, of course, find holes in the simplifying assumptions I have made here, but it doesn't really matter if that number instead is 1 in 1000 or 1 in 10000. The basic point being made here is just that the odds are heavily stacked against new ventures being successful. But that's also one of the distinguishing characteristics of entrepreneurs -- to go ahead and try to bring their idea to life despite the heavy odds.
Sources of some of the numbers:
Here are others' calculations of the odds that lead to a similar conclusion:
1.Dear Entrepreneurs: Here's How Bad Your Odds Of Success Are
2.Why 99.997% Of Entrepreneurs May Want To Postpone Or Avoid VC -- Even If You Can Get It
It'd be impossible to get a real number for this, but generally 700 out of 1000 real startups (not counting the ones not taken seriously by their own founders) fail completely. 299 get ok to good returns for founders and investors. 1 ends up like the Facebook, Instagram, Twitter, etc of the world.
I have been involved in many startup and early stage companies as a founder, angel, investor and advisor. I have a broad range of contacts and have been investing for more than 30 years. Its more likely that a random High School basketball player will be the MVP in the finals than any random startup will be a headline success story. There are probably many tens of thousands of abject business failures across the country for every success story in Silicon Valley. And that's just the abject failures-thats not even counting the living dead companies which never achieve what they set out to do but which don't close their doors. For every unicorn, there are probably a million business failures. And to be clear, failure is rarely equivocal.