You really cant. People grow up and they grow apart: they want different things and thats fine but you cant stop them from living their own life. And precisely how are you supposed to know these things if you marry someone straight away? You need to know how they act around children, their friends and family, your friends and family and how they treat their equals or your waiter all of these are tell-tale signs to see if youre compatible. What if you get married and then you find out that they dont like Harry Potter or the Lord Of The Rings or Friends or the worst case scenario: what if they dont like all three? You might think that grounds for annulment, but the government probably won't, because their priorities are badly broken. And lets face it, it isnt true love until you can perform all bodily functions in front of each and still want to have sex with them afterwards.