I don't know, and the specific percent isn't the point. I'd encourage you to critically read bios of any Silicon Valley idols you might have, with an eye towards this.
My personal epiphany came about 10 years ago. I was in an incubator in SF, and some investor came to give a talk about fundraising. They heavily emphasized that many startups do a friends-and-family round to bridge them to a proper seed round-- nothing major, just get 20k from 5 family members and you should be good until you have something to show angel investors. My two co-founders and I (all from the Midwest) realized that we couldn't even come up with five people to ask for 20k because all of us came from pretty modest families.
These are the types of privileges that get glossed over in success stories. To be successful you, more likely than not, need to either have money or have connections to money. Everyone likes a good underdog story, but those founders are more like lottery winners than anything else.
So, coming from that lens, it's hard to take advice seriously from "successful" entrepreneurs. It's sort of our industry's equivalent of "just stop eating avocado toast and you'll become a millionaire."