I disagree. I think that it's who you know.
But this is not-- by a long shot-- how most startups become successful.
And one thing I've learned in the last 20 years-- the people who are worth knowing-- the really valuable ones-- they are approachable. You don't need someone to make an introduction to them.
Universally people who make their living as middlement and introduction brokers are people who are selling you something you could get for free, and undermining your ability to use it at the same time (because they are selling it to others as well-- making their introduction less valuable than contacting the person cold.)