Like when there's a friend of your working on his startup idea and asking you to join as a cofounder. At this stage there's nothing to gauge (not even a company yet).
You can't. Otherwise all of us would be billionaires.<p>There is a ton of risk not matter. We hear from a lot of people who "always knew they had it." But there are a ton of failures who also believed "they always had it" before failing.