*You must ensure that the love interests don't know which one of them you like more (The 1st blind).
*Equally you yourself should be unaware which one you actually preference more (The 2nd blind).
Results are highly successful for ending up with one person at least on a given night due to jealousy created.
M: Ended up with Maria.
H: Pulled a double blind with her and Katie.
M: I see... smarmy bastard.