Nah, I don't think you "just know," or at least I don't usually believe people when they say that until they've been married for 10+ years.
But I'm cynical, and I've never "known" much about anything in my life, so I have learned/am learning to just wait things out until I'm ready to jump and take a risk.
Again, I think very few people "know;" but many people know when they've met the person they are willing to take a flying leap with.
