@Moon @noelle Here's the argumentation:

Professional angel investors, presumably good at determining all the knowable factors that would cause a startup to fail, still only see 10% of their investments succeed. They have access to people with experience in business development and execution that can help their investments prosper.

The difference between those 10% and the other 90% would be things nobody could foresee, not things like talent, connections, market knowledge, grit etc. It would be unforeseeable factors like being in the right place at the right time. Luck.