With YieldStreet, you're betting on the skill of the jockey (the manager of the investment) and the skill of the platform (YieldStreet) in screening out the bad loan applications. You're also betting on the common sense of the investor to put only a small amount of their investment capital on the line (money they can afford to lose).
I'm not in a position to judge the merits of any particular investment myself ("I don't know jewelry"), but I can make sure I trust the platform ("know the jeweler"). I haven't actually made any investments yet, but I have money staged on the site to be ready when the right one for me comes along.